Abstrac&The effect of different particle size distributions (PSD's) on kinetic behavior in stirred-batch adsorption systems was investigated by numerically modeling the uptake of p-nitrophenol from aqueous solution by granular activated carbon in a well-stirred batch type of environment. Four different Gaussian PSD's, two different log-normal PSD's and one case of uniform particle size were studied. The model accounted for both external and internal mass transfer resistances, and for the highly nonlinear equilibrium relation which characterizes the p-nitrophenollactivated carbon system. AU isotherm parameters and "base-case" kinetic parameters were experimentally determined values (from the literature). The kinetic parameter values were varied in some cases to assess their intluence. Moreover, both infinite-bath and finite-bath situations were evaluated. The modeling results show that the different particle size distributions did not generally give kinetic behavior widely different from the uniform particle size case when an infinite bath was assumed. However, for the more realistic case of a finite bath, the different PSD's gave significantly more distinctive results, especially for fractional mass uptake values greater than about 0.7. It is concluded that, in finite bath experiments, the nature of the adsorbent PSD must be accounted for in interpreting data obtained at fractional mass uptake values greater than about 0.7, unless the adsorbent PSD is reasonably narrow.