Fasudil-containing preparations that despite the us of a container excelling in the visibility of contents without particularly blocking of light, exhibit high stability against light; and a method of improving the stability of the preparations against light of storing the same. By regulating the pH value of aqueous solution of fasudil charged in a colorless transparent container to .ltoreq.5.5, there can be provided fasudil-containing preparations excelling in stability against light; and can be provided a method of improving the stability of the aqueous solution of fasudil against light, or storing the same.