In the present study, analysis and source apportionment of the elemental composition of PM was conducted in the urban atmosphere of Karachi. Trace elements such as Ni, Ba, Cd, Ca, Mg, Cr, Mn, Fe, Co, Cu, Sr and Ti were measured. The PM concentration ranged from 255 μg m to 793 μg m, with an average of 438 ± 161 μg m. Among the various elements analyzed, concentrations of Ca, Al and Fe were the highest (> 10000 ng m), followed by Mg and S (> 1000 ng m). Elements such as Zn, P, Cu, Pb, Mn, Ti, Sr and Ba demonstrated medium concentrations (> 100 ng m), whereas the lowest concentrations were found for elements such as Cr, Ni and Se (> 10 ng m). The Positive Matrix Factorization (PMF) model identified five possible factors that contributed to PM, namely, biomass burning, coal combustion, resuspended road/soil dust, vehicular emissions and industrial dust. Industrial dust was the highest contributor (23.2%) to PM followed by Biomass burning (23%), Vehicular emissions (22.2%), Coal combustion (21.7%) and Re-suspended dust (9.9%). A strong positive correlation (R = 0.98) was observed between the model predicted PM mass and the gravimetrically measured mass collected on filters.