The chemical characteristics,oxidative potential,and sources of PM2.5 were analyzed at the urban sites of Lahore and Peshawar,Pakistan in February 2019.Carbonaceous species,water soluble ions,and metal elements were measured to investigate the chemical composition and sources of PM2.5.The dithiothreitol(DTT)consumption rate was measured to evalu-ate the oxidative potential of PM2.5.Both cities showed a high exposure risk of PM2.5 re-garding its oxidative potential(DTTv).Carbonaceous and some of the elemental species of PM2.5 correlated well with DTTv in both Lahore and Peshawar.Besides,the DTTv of PM2.5 in Lahore showed significant positive correlation with most of the measured water solu-ble ions,however,ions were DTT-inactive in Peshawar.Due to the higher proportions of carbonaceous species and metal elements,Peshawar showed higher mass-normalized DTT activity of PM2.5 compared to Lahore although the average PM2.5 concentration in Peshawar was lower.The high concentrations of toxic metals also posed serious non-carcinogenic and carcinogenic risks to the residents of both cities.Principle component analysis coupled with multiple linear regression was applied to investigate different source contributions to PM2.5 and its oxidative potential.Mixed sources of traffic and road dust resuspension and coal combustion,direct vehicle emission,and biomass burning and formation of secondary aerosol were identified as the major sources of PM2.5 in both cities.The findings of this study provide important data for evaluation of the potential health risks of PM2.5 and for formu-lation of efficient control strategies in major cities of Pakistan.