The effect of grinding in an agate centrifugal ball mill on the transformations of polymorphs of chloramphenicol palmitate (CPP) were studied by means of X-ray diffraction analysis, infrared (IR) spectroscopy and differential scanning calorimetry (DSC). Three kinds of the polymorphs of CPP were reported, that is, forms A, B and C. There was no change in the X-ray diffraction profile of form A (stable form) on grinding for 600 min, but its profile became broader than that of intact form A. There was no change in the X-ray diffraction profile of form B (meta-stable form) on grinding for 130 min, but form B was transformed into form A by grinding for more than 140 min. Form B ground for 140 min contained about 35% form A ; when ground for 150 min, it contained about 80% form A, and when ground for more than 150 min, it contained a constant level of about 80% form A. The X-ray diffraction profile of form C (meta-stable form) suggested that form C was transformed into form B by grinding for 20 min ; thereafter the product was transformed into form A by grinding for 160 min. Form C ground for 4 min contained about 60% form B ; when ground for 20 min, it contained about 100% form B, and ground for 160 min, it contained about 80% form A. These results suggest that the transformations of polymorphs of CPP by grinding are form C→form B→form A. The melting point (mp) and the heat of fusion (H) were measured by DSC. The mp and the H of form A obtained by grinding were about 2.5°C and about 2.5 kcal/mol lower than those of intact form A, respectively, and the solubility in 50% (v/v) aqueous isopropyl alchohol was about twice that of intact form A.