Three new polymorphic modifications were prepared by recrystallization under various conditions and characterized by DSC and X-ray crystallography. In pH 4.0 buffer at $37{pm}0.5^{circ}C$, the polymorphic modifications showed significant differences in the dissolution rate. The dissolution rate of Mod. 4, amorphous form, was faster than that of marketed cefaclor (Mod. 1). When all modifications were stored at 52% RH, 95% RH and in silica gel desiccator, any polymorphic transformation was not observed.