Abstract: AIM: To study the polarographic behaviour and reduction mechanism of medroxyprogesterone acetate (MPA) in acetate buffer solution. A new method for the determination of MPA was established by linearsweep polarography. METHODS: Fast scan cyclic voltammetry, controlled potential electrolysis, linearsweep polarography and ultravioletvisible spectrophotometry were used in the present research. RESULTS: The C=C bond of MPA first undergoes a 1 e, 1H⁺reduction to form a radical HMPA·, then the further reduction of HMPA· in 1 e, 1H⁺ process is simultaneous with the dimerization reaction between HMPA· and the neutral molecule MPA. In 0.2 mol·L^-1 HAc—NaAc (pH 5.0) buffer solution, the reduction wave (E_P=-1.33 V, vs.SCE) of MPA can be used for analytical purpose. The secondorder derivative peak current of MPA is linear with the MPA concentration over the range of 2.0×10^-6～6.0×10^-5 mol·L^-1. The linear regression equation is iP″(nA)=5.81+6.8×10⁵C_MPA (mol·L^-1), and the correlation coefficient γ=0.998. The detection limit is 8.0×10^-7 mol·L^-1.CONCLUSION: The characteristics of the polarographic reduction of steroids was elucidated. The process of reduction was the two step transmission process of electric charge with the intermediate free radical.