The objective of this investigation is to evaluate the influences of natural sorbent particle size and system Ca2+ concentration,on sorption of low-polarity organic chemicals. The physicochemical properties of the different particle size soil and sediment subsamples and the surface characters of the soil and sediment samples in various CaCl2 concentrations were determined. The sorption behavior of phenanthrene (PHN) on the subsamples of different particle size and to the samples in various CaCl2 solutions was examined. Batch experiments demonstrate that the sorption capacities increase with decreased particle size for both soil and sediment. It is presumably due to the higher total organic carbon (TOC) content for the finer particles. But the enhancements in sorption coefficients are not met with the equal increases in TOC contents. The effect of Ca2+ on PHN uptake is strong in short contact time but slight in long contact time. With increasing Ca2+ concentration, the sorption capacities for Beizhai soil increase first in the low Ca2+ concentration range, and then decline. Nevertheless,. the increase of Ca2+ concentration greatly reduces the uptake of phenanthrene on Guanting sediment over the overall measured range. The different physicochemical properties, such as dissolved organic carbon (DOC) content, mineral and element composition, and surface characters, between soil and sediment may result in this discrepancy. (C) 2003 Elsevier Inc. All rights reserved.