Urban air quality is increasingly being studied as a fraction of the world's population is now living in megacities. In this study, particulate matter (PM) along Taft Avenue, Manila, Philippines, is investigated in terms of its ability to induce genetic damage on human peripheral blood lymphocytes (PBL). Size-segregated roadside air samples were obtained from 2015-2016 near the university gate and analyzed using in vitro micronucleus and cytokinesis-block proliferation tests. While cellular proliferation was unaffected by 0 – 0.1 kg·m-3 of PM1.0 and PM2.5, PBL cells treated with PM2.5 displayed significantly higher micronucleus count (p = 0.03) compared to the cells treated with PM1.0. Atomic Absorption Spectroscopy revealed greater amounts of Cd, Ca, Pb, K, Na, and Zn in PM2.5 compared to PM1.0. The results indicate the differences in composition of the two size fractions of air particulates are associated with their genotoxicities.