Abstract: A sensitive and rapid methed for the determination of azathiopurine concentrationin human serum was establiShed.By using ultraviolet second derivative spectra,the method eliminatedbackground interference of biological sample and coexisting drugs.The serum sample was extractedwith ethyl acetate,the extract was evaporated to dryness with a gentle N₂ stream,and 0.25ml ofmethanol was added to disSolve the residue.Quantitative calculation was made with anal vticalwavelength of 274 nm and 293 nm,and peak-to- valley method.The minimum detectableconcentration of AZP in serum was 25 ng· ml^-1 and average recovery was 99.3%±5.9%。