Rasilez^® tablets (RTs) contain the active ingredient aliskiren, which is a direct renin inhibitor of the renin-angiotensin system and used for the treatment of hypertension. We examined the influence of temperature and humidity on the physico-pharmaceutical characteristics (mass, volume, hardness, elution) of RTs. The RTs were preserved under conditions in which the temperature and humidity were altered using the second-order spherical composite experimental design for multi-objective problems. The characteristics of RTs were influenced more by the humidity than temperature, and differed markedly with over 55% relative humidity (RH). The mass and volume were increased with increasing humidity, and the tablets swelled. The hardness after vacuum-drying of the tablets, which preserved moisture conditions, was increased. Semitransparent particles were observed in the cross-section of the drying tablets in which aliskiren crystal forms were changed to amorphous forms. The mean dissolution time (MDT) of tablets was reduced with increasing humidity. The critical relative humidity (CRH) of the tablets was 36.1%RH at 30°C. These results suggest that RTs, on moisture absorption, showed changes in not their appearance and hardness, but also in crystal forms and the elution characteristics of aliskiren.