Light scattering coefficient of visible light by atmospheric aerosol over the size range 0.01-10$mu$m is determined from scattering efficiency and aerosol size distribution. Aerosol number distribution as a function of particle diameter dN/dlog D decreases rapidly as increasing particle size. Distribution of scattering coefficient d$sigma_s/dlog$ D is mostly accumulated in diameter 0.1-2.0 $mu$m showing its maximum in the vicinity of 0.6$mu$m. This means that the visible light in the atmosphere is mainly scattered by these particles. Diurnal variation of scattering coefficient $sigma_s$ appears its maximum in the morning, while minimum in the afternoon which agrees with the aerosol number distribution in the size range 0.1-2.0 $mu$m.