Using a Shosaiko-to extract granule, we investigated the effects of the timing of administration (orally, before and after a meal) on the plasma concentration of its active constituents, glycyrrhizin (GL), baicalin, baicalein and glycyrrhizic acid (GA), a metabolite of GL. The pattern of plasma concentration change of GL differed between the two times of administration, and followed a two-phase pattern when the granules were taken before meals. There was no difference neither in the area under the plasma concentration-time curve (AUC) between the two periods, nor AUC itself. GA showed no difference in plasma concentration pattern, nor was baicalin detected in the plasma following administration by either method. The plasma concentration pattern of baicalein differed between the two timings but followed that of the two-phase pattern in each case. The plasma concentration pattern of active constituents of Shosaiko-to extract granule varied with the time of administration, but there was no significant difference in the maximum plasma concentration or AUC of active constituents depending on the administration. We concluded that the present clinical timing of administration of Shosaiko-to should be determined on the basis of patient compliance and other relevant factors.