Background: Studies have identified associations between air pollution and lipid levels in adults, suggesting a mechanism by which air pollution contributes to cardiovascular disease. However, little is known about the association between early life air pollution exposure and lipid levels in children. Methods: Participants included 465 mother-child pairs from a prospective birth cohort in Mexico City. Daily particulate matter <2.5 m in diameter (PM 2.5) predictions were estimated using a satellite-based exposure model and averaged over trimesters, the entire pregnancy, and the first year of life. We assessed associations with several lipid measures at 4-6 years of age, including total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), non-HDL-C, high-density lipoprotein cholesterol (HDL-C), and triglycerides (TG). Linear regression models were used to estimate change in lipid levels with each interquartile range increase in PM 2.5. We additionally assessed if associations between PM 2.5and lipid levels varied across lipid quantiles using quantile regression. Models were adjusted for maternal education, body mass index, and age, child's age at study visit, prenatal environmental tobacco smoke, and season of conception. Results: PM 2.5exposure during the third trimester was associated with increases in childhood total cholesterol, LDL-C, and non-HDL-C, and decreases in HDL-C and triglycerides. There was additionally an increasing trend in the effect estimate across higher quantiles of total cholesterol, LDL-C, and non-HDL-C during the third trimester and entire pregnancy period. There were no consistent associations for first year of life exposures. Conclusion: In this longitudinal birth cohort in Mexico City, associations between prenatal PM 2.5and childhood lipid (total cholesterol, LDL-C, non-HDL-C) levels were greater for children at higher lipid quantiles.