Dependence of interaction force between condensed polystyrene-latex (PSL) particles and atomic force microscope (AFM) tip on diameter of PSL particle is studied from the force curve measured in dry atmosphere. In the diameter range of PSL particle from 42 nm to 1 μm, it is found that this dependence is different from that of geometric mean radius which is derived from DMT theory. These results can be analyzed in terms of PSL particle deformation effect and contribution of surrounding PSL particles.