Respiratory diseases morbidity and mortality rate of children between 0-5 age is considerably high in the US, China and East Asian countries. Studies conducted in Mongolia reveals that respiratory diseases morbidity rate of children between 1-4 age is very high in UB. Respiratory diseases case of children aged between 0-5 is predominantly registered in UB. Recent trend suggests that respiratory disease case of children aged between 0-5 shows no sign of decreasing, instead it is increasing. In addition to virus and bacteria, social factors have been one of the main influencers to respiratory diseases morbidity among small children, it was concluded.

Rationale: The most common reasons of childhood deaths is Respiratory Tract Infections and every year, 3 million out of 5 million children under five years of age suffering from respiratory diseases die due to lung inflammation (Stansfield et al, 1993).
In Ulaanbaatar live 182016 children aged 0-4 years and it around 45 percent of the total population in 2018. Ulaanbaatar is ranked first place in the world by air pollution, especially, atmospheric particulate matter (PM2.5) are much higher than the average annual concentrations indication in the recommendations of World Health Organization. This brings high risk of respiratory diseases morbidity and mortality to the children.
It is need to study the last ten-year trend of respiratory diseases which to happen to the children under five years of age, and it should be reduced the respiratory illness of young children. Objective: To study the last ten-year morbidity and mortality trend of respiratory diseases among children aged 0-4 in Ulaanbaatar. Methodology: We have been investigated the trend-survey of the respiratory disease morbidity and mortality of children aged 0-4 in Ulaanbaatar based on the last ten-year statistical data of the Ulaanbaatar Health Department. The population was estimated at 10000 people. Result: Hospital admissions because of respiratory diseases of children under 5-year-old were 3629,9-2009; 3827,3-2010; 3890-2011; 3958,3-2012; 4825,7-2013; 5723,5-2014 4669,4-2015; 5839,3-2016; 5624,4-2017; 4754.9-2018; 3811-2019 respectively, per 10000 people in Ulaanbaatar. The number of hospitalized patients due to respiratory diseases of Ulaanbaatar is increasing gradually from 2009 to 2019.
Respiratory disease mortality was 20,8 in 2008; 21-2009; 20,6-2010; 16,2-2011; 16-2012; 16,4-2013; 17,8-2014; 17,3-2015; 18,2-2016; 15,4-2017; 16.1-2018; 14.1-2019 respectively and mortality rate has been slightly decreased in recent years. Conclusion Although respiratory illness of children aged 0-4 in Ulaanbaatar has been steadily increasing over the past decade, the children mortality has been decreasing in recent years, gradually. Furthermore, it shall be studied of air quality and outdoor indoor air pollution-related diseases among children, detailed.