The method to estimate hygroscopicity of pharmaceutical products in powder or granule has not been established. In this study, changes in weight and fluidity of 10 commercial dry syrup preparations (fine granules to be prepared into a liquid form) were examined after storage with and without addition of sulpyrine powder. The samples were stored in 8 grades of relative humidities ranging from 56.3 to 100.0 % at 30°. When the data from each of the samples were plotted with weight increased (%) as ordinate and relative humidity (%) as abscissa, the hygroscopic curves were obtained respectively. From the curves, 3 kinds of values (θ, RHs, RHs') were selected to indicate the characteristics of hygroscopic changes of each sample. These values were considered representative of hygroscopicity of powders or granules unless formulations were changed. For protecting them from environmental water after repackaging, diluting or mixing with another product, they should be stored in the condition of lower humidity than RHs.