Abstract: Charge transfer reactions between either of the 2 hyperglycaemia drugs,metformin hydrochloride and repaglinide (as electron donor) and tetrachlorobenzoquinone (as electron acceptor) were studied spectrophotometrically.In a borax buffer of pH 9-10,a colored and stable charge transfer complex,with molar ratio of 1 to 1 was formed between either the metformin or repaglinide and tetrachlorobenzoquinone,when the reactants were kept in a water bath at 25 ℃ for 15 min.Absorption maxima of the complex of metformin was found at the wavelength of 695 nm,and of the complex of repaglinide at the wavelength of 718 nm.Linearity of the calibration curve was found in the range within 1.0×10-3mol·L-1 for metformin and in the range within 2.0×10-4mol·L-1 for repaglinide,with values of apparent molar absorptivity 4.11×104L·mol-1·cm-1 and 3.08×104 L·mol-1·cm-1 respectively.The proposed method was applied to the analysis of 3 drug samples,giving results in consistency with the results of pharmacopoeia method (as proved by t-test),and values of RSD′s (n=5) less than 3.5%.Results of test for recovery obtained were 98.6% (average) for metformin and 102.8% (average) for repaglinide.