For the determination of vitamin A in pharmaceuticals, Mulder's method has advantages in rapidity and precision, compared with U.S.P. method. But Mulder's method tends to give higher values, which vary according to the forms of preparations. The authors proved that the cause of higher value was chiefly in the washing process by KOH, i.e. benzene was dissolved into water phase to some extent while vitamin A not, thus resulting in a relative concentration of vitamin A. This phenomenon was not recognized in the use of cyclohexane instead of benzene as extracting solvent. The cyclohexane method was applied to U.S.P. vitamin A reference standard and various forms of vitamin A preparations, and it was proved that the results were in good agreement with those of U.S.P. method.