The effect of firework activities on air quality was assessed from the ambient concentrations of PM10, water soluble ionic species, metals and SO2 over Kolkata metropolis, India during Diwali festival in November 2010. PM10 concentrations on Diwali night were found to be ~5 times higher than the normal day night-time average concentration. The increase in night-time concentrations of the metals on Diwali spanned over a wide range (Al, Zn, Pb and Cd showed 5–12 times, Cu, Fe and Mn showed 25–40 times and Co and V showed 70–80 times increase in concentrations) compared to night-time concentrations on normal day. The water soluble ionic species showed 1.5–6 times higher concentrations on Diwali night than normal day. The remarkable increases were found for K+, Ca2+, Mg2+ and SO42–. The diurnal variation of PM10 and SO2 was also studied in one of the sites which showed their maximum concentrations on Diwali night during 8 P.M.–3 A.M. indicating maximum firework activities during this period. PM10 and SO2 concentrations increased by ~5 times than normal day during this period at this site. The extensive use of firecrackers during Diwali festival was found to have significant effect on the high increase of these air pollutants which could be associated with the serious health impacts and thus use of firecrackers in this kind of festival in a highly populated metro-city like Kolkata, India needs to be controlled where air pollution is an acute problem through-out the year.