A compound having structures of both vitamins E and C, L-ascorbic acid dl-alpha-tocopherol phosphoric acid diester potassium salt (EPC-K), which was proven to have both anti-oxidative3%!d moisturizing effects, has been formulated in the quasi drug hair growing products to mainly prevent dandruff and itching which may be one of the causes for the hair loss. Stabilities of EPC-K in 75% ethanolic solutions with various pHs (2-10) were examined extensively by storing them at 50 degrees C for 30 d and by sunlight exposure for 30 d. Decomposition of EPC-K was only observed under pH 2 at a level of 50% and under sunlight exposure at 25% level. A main decomposition product was identified as tocopheryl phosphate (EP), suggesting that a decomposition route was through hydrolysis. EPC-K was found to decompose by as much as 20% under 30 d storage at 50 degrees C when the concentration of the aqueous ethanolic solution was 0-30%. 1H, 13C and 31P-NMR studies in addition to a micelle formation test using pyrene fluorescent probe revealed that EPC-K formed a micelle at such low concentration of ethanol, which was assumed to be a cause for unstableness of EPC-K in that range. Hydrolytic decomposition of EPC-K was found by the reaction rate study to be a pseudo first order reaction with activation energy of 16.98 kcal/mol.