PURPOSE: To efficiently produce the oral medicine solution which persistently has its physiologically active activity even under the condition of relatively high temperatures and which contains a sennoside compound exhibiting excellent quality stability as an active ingredient.

CONSTITUTION: A solution containing as an active ingredient a sennoside compound which is a medicinally active ingredient of Cassia angustifolia Vahl., Rheum spp., etc., and whose quality is extremely unstable under the conditions of relatively high temperatures is (a) filtered through a porous filtration material, preferably a filtration material used for micro-filtration, ultrafiltration, reverse osmosis, etc., and having pore diameters smaller than 0.45μm. especially a membrane filter, in a state free from the generation of precipitates, or (b) brought into contact with and passed through an adsorbent comprising an inorganic or organic porous material, preferably silica gel, alumina, porous polymer beads, etc., capable of being used as a polymeric carrier for filtration (especially a column filler for separation) to obtain the objective oral medicine solution which contains the sennoside compound as the active ingredient and whose physiological activity is not inactivated over a long period of six mouths even after stood at a high temperature of 40°C. The treatment process (a) may be added before and/or after the treatment process (b) in series.