In this work a novel method for the determination of tamoxifen in flow-injection systems has been developed. The fast Fourier transform continuous cyclic voltammetry (FFTCV) at gold microelectrode in flowing solution system was used for determination of tamoxifen in its pharmaceutical formulations. The developed technique is very simple, precise, accurate, time saving and economical, compared to all of the previously reported methods. The effects of various parameters on the sensitivity of the method were investigated. The best performance was obtained with the pH value of 2, scan rate value of 50V s-1, accumulation potential of 0 mV and accumulation time of 0.5 s. The proposed method has some advantages over other reported methods such as, no need for the removal of oxygen from the test solution, a picomolar detection limit, and finally the method is fast enough for the determination of any such compound, in a wide variety of chromatographic methods. The method was linear over the concentration range of 1875-78000 pg/ml (r = 0.9980) with a limit of detection and quantitation 37.1 and 200 pg/ml, respectively. We used this method to determination of tamoxifen in tablets.