Abstract: In a pure aqueous medium,a charge transfer complex with mole ratio of 1 to 1 was formed between the drug,centrophenoxine,and alizarin red,giving negative absorption maximum at the wavelength of 518 nm,and positive absorption maximum of alizarin red at 420 nm.Linear relationship between values of ΔA (i.e.,the difference between absorbances of blank solution and test solution,A0-Ai) and the mass or concentration of centrophenoxine was found in ranges of 20-250 μg or 4.0-50.0 mg·L-1 respectively.The proposed method was used in the determination of centrophenoxine contents in its injections and capsules,the results obtained were in consistency with those found by the pharmacopoeia method.