In the present study, elemental composition of PM10 and source apportionment 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 PM10 concentration ranged from 255 µg m–3 to 793 µg m–3 with an average of 438 ± 161 µg m–3. Among the various elements analyzed, concentrations of Ca, Al and Fe were highest (> 10 000 ng m–3), followed by Mg and S (> 1000 ng m–3). Elements like Zn, P, Cu, Pb, Mn, Ti, Sr and Ba demonstrated medium concentrations (> 100 ng m–3), whereas lowest concentrations were measured for elements like Cr, Ni and Se (> 10 ng m–3). The Positive Matrix Factorization (PMF) model identified five possible factors contributing towards PM10, including biomass burning, coal combustion, re-suspended road/soil dust, vehicular emission and industrial dust. Industrial dust as major contributor (23.2%) to PM10 followed by Biomass burning (23%), Vehicular emissions (22.2%), Coal combustion (21.7%) and Re-suspended dust (9.9%). A strong positive correlation (R2 = 0.98) was observed between the model predicted PM10 mass and gravimetrically measured mass collected on filters.