The dissolution rate of medical tablets has hitherto been measured by repeating dissolution tests, which require considerable time to get experimental confirmation of dissolution characteristics. Thus, it has not been investigated from the viewpoint of prescription of the dissolution rate. In this paper, the effects of tablet compaction and primary-particle properties on the dissolution rate were studied experimentally and quantitatively. It was found that the dissolution rate increased with increasing voidage of the tablet, increasing shape index of primary particles, decreasing active component and with decreasing specific surface diameter. The effect of shape index should, therefore, be considered by constructing a new dissolution model, because it is of an equal level to the effect of the specific surface diameter.