The results demonstrated that the total content of rhinacanthins was significantly decreased under all tested pH after 2 weeks of storage. Rhinacanthin-C content was significantly decreased after 1 week of storage at pH 7.0 and 8.0 and after 2 weeks of storage at pH 5.5 ( Table 5). The content of rhinacanthin-D was significantly decreased after 2 weeks of storage at pH 8.0 and after 3 weeks of storage at pH 5.5 and 7.0 ( Table 6). Rhinacanthin-N content was significantly decreased after 1 week of storage at all tested pH conditions ( Table 7). It implies that all rhinacanthins are not stable when they are prepared as an aqueous alcoholic solution. However, the rhinacanthin solution at pH 5.5 was more stable than those at pH 7.0 and pH 8.0. The instability of rhinacanthins in the solution should be considered as their hydrolysis of the rhinacanthins. Thus, preparation of the RRn extract in an aqueous solution should be performed carefully.