A new mathematical equation characterizing the compression of pharmaceutical materials is presented.  This equation presumed that the rate of change of the compressible volume of powder with respect to the pressure is proportional to the compressible volume.  The new model provided a good fit to several model substances employing non-linear regression techniques.  The validity of the model had been verified with experimental results of various pharmaceutical powders according to the Akaikes informatics criterion (AIC) and the sum of squared deviations (SS).  The parameter of the new model might reflect quantitatively the fundamental compression behaviors of the powders.  It had demonstrated that the proposed model could well predict the compaction characteristics of solid particles like the Kawakita model.