The research of behavior of cefixime in biological media was conducted by spectrophotometric method. It was shown that the maximum of light absorption of cefixime against the background of oral fluid is observed at ? = 292 nm and for blood serum at ? = 289 nm. The interval of linear dependence optical density – concentration of cefixime is 3–50 mkg/ml. The optimal conditions of precipitation of proteins in the studied biological media were revealed.