Abstract: AIM: To study the electrochemical reduction and direct measurement of theophylline. METHODS: The electrochemical behavior of theophylline was studied with multi semi differential electrochemical instrument, the reversibility of electrode reaction and the electro reduction mechanism were investigated with cyclic voltammetry and UV spectrometry, respectively. RESULTS: In phosphoric acid medium, a reductive peak was observed at-1.08 V . The peak current was proportional to the concentration of theophylline over the range of 2.0×10^-6～2.0×10^-4 mol·L^-1 . CONCLUSION: The double bond on C₈-N₉ in theophylline molecular structure can be reduced directly on mercury electrode under suitable conditions. The electrode reaction was irreversible. This method has been shown to be adequate for the direct determination of theophylline.