Over the last decade a large number of studies have investigated the possible adverse effects of ambient air pollution on birth outcomes. For preterm births the evidence as yet is insufficient to their infer causality. Our study goal was to study the associations between air pollution exposures during pregnancy and preterm birth for a 6 years period (January 2008 through December 31, 2013) in Ulaanbaatar, Mongolia. We used a logistic regression adjusting for gestational age, parental education level, parity and infant age. The preterm birth varied with maternal age, maternal education level, maternal pregnancy order and season after adjusting covariates. Young maternal age, maternal less education level, early and older birth order, spring season, not married status and higher number of pregnancy order t are risk factors for low birth weight. The correlation of preterm birth and air pollution was observed in the second and the third trimester of pregnancy. The preterm birth rates were associated with the average of combined air pollutants concentrations such us PM10, NO2 and SO2 in the preceding 6 weeks.