The United States and Russia verbally dueled before the vote, which called for a seven-day truce. Venezuela also rejected the resolution.
came as the Syrian regime continues to blitz Aleppo's east in support of its troops there, as part of an operation to seize control of the area held by rebels for more than four years.
While the regime has made sweeping territorial gains in eastern Aleppo, rebel forces fought back Monday in the al-Mayassar neighborhood. Rebels also hit a Russian mobile hospital in Aleppo, killing two female medics and injuring another pediatrician, Russia's Defense Ministry said in a statement.
A government siege on eastern Aleppo is tighter than ever, and food stocks, clean water supplies and medicine are running dry. The United Nations has repeatedly called for safe passage for its humanitarian staff, but it said the Syrian government and its most powerful ally, Russia, have failed to guarantee that.
Russia has begun sending in aid and setting up mobile clinics, after hospitals in eastern Aleppo were bombed beyond use. Russia has been widely blamed for the destruction of medical facilities. It has supported Syrian government troops with an aerial bombardment campaign.
Disagreement in the Security Council
It was the sixth Russian veto since 2011 on a Syria-themed resolution. China joined for the fifth time.
Years of disagreement among major powers on Syria spilled over in the Security Council before and after the veto.
Russia claimed there was progress being made in talks between Russian Foreign Minister Sergey Lavrov and US Secretary of State John Kerry and that calling for a vote was a bad tactic. But the deputy US ambassador, Michele Sison, responded, "That is a made up alibi."
Sison told the council the United States and others backing the resolution were not going to let Russia "string along" the Security Council while waiting for a compromise from the Russians that never seems to come.
The draft resolution demanded that all parties in the conflict allow immediate and safe humanitarian access to all of Aleppo for the United Nations and its partners.
It did not include groups the council categorizes as terrorist organizations, such as ISIS and the Al-Nusra Front.
The United States and Russia announced Saturday they were working together on an agreement to have all rebel groups expelled from eastern Aleppo and to ensure safe delivery of aid there by humanitarian staff. The United States had armed groups there it considered moderate, while Russia targeted the same groups with airstrikes to prop up the Assad regime.
Lavrov, speaking at a news conference in Moscow before the vote, argued that a ceasefire would also give rebels the chance to regroup and strengthen.
He said Moscow and Washington planned talks on the routes and timing of the withdrawal of rebels.
"Once they're set, a ceasefire regime will come into force to start the evacuation of these armed groups. If US-Russian cooperation on this will bring results -- and we have all reasons to believe it will do so -- then the problem of eastern Aleppo will be effectively solved," he said, adding it would allow "smooth humanitarian aid delivery" and normalize life there.
The 15-member Security Council has faced widespread criticism over its failure to find a political solution to the Syrian war, which has left an estimated 400,000 people dead. Even agreeing on terms to allow an occasional aid delivery often takes weeks or months.
Regime takes 60% of eastern Aleppo
Thirty-two civilians were killed and 115 injured Monday in Aleppo, while 67 people were killed and 80 injured on Sunday in airstrikes that targeted residential areas, marketplaces and schools, according to the self-styled Syrian Civil Defense rescue group, also known as the White Helmets.
The regime now holds some 60% of eastern Aleppo, making swift gains since breaking through rebel defense lines.
Hundreds have died since regime forces entered eastern Aleppo, according to activist groups, while around 30,000 civilians have now fled, some of them reviling the rebels who they say wouldn't let them leave, and others condemning the regime for the decimation of their homes and the high human toll from the airstrikes.
'We will rebuild'
Regime forces captured the entire northeast in the first few days, including its largest district, Masaken Hanano, where civilians are starting to return.
Khaled Chobello is one of those residents, coming back for the first time since he fled in 2012, when rebels took over eastern Aleppo.
Masaken Hanano has been largely reduced to rubble, and Chobello's apartment is now a chaotic mess, with holes through the walls and his possessions thrown into a heap.
"I'm very sad because everything is either destroyed or ransacked," he said.
One of the few possessions of value found under the rubble was a photograph of his family.
"The walls are destroyed, but we will come back here and rebuild."