Protesters, some wearing face masks and holding black balloons, gathered as temperatures fell below -20C.
Ulaanbaatar, one of the world's coldest capitals, is also one of the most polluted cities in the world, according to the UN children's agency Unicef.
Many residents burn polluting fuels to keep their homes warm.
Some say they cannot afford the alternatives and have asked for state assistance.
One protester's banner read: "Wake up and smell the smog."
It is the second pollution protest during the current Mongolian winter.
In December, Mongolian environment and tourism minister Oyunkhorol Dulamsuren said that, between 2011 and 2015, the government spent more than $37m, plus $47m from international donors, on tackling air pollution.
Among children under five, respiratory infections are one of the leading causes of death, Unicef says.
Thousands of Mongolians took to the streets of the capital, Ulaanbaatar, on Saturday to call for the government to take action on air pollution.