Abstract: Graphene (GR) and still further a composite material of GR/PDDA were prepared from graphite oxide (GO) with the green reductant, polydiallyl dimethyl ammonium chloride (PDDA). A suspension of 0.5 g·L^-1 GR/PDDA in water was applied onto the surface of pretreated GCE dropwise, and dried under radiation of infrared lamp, thus to obtain the composite modified electrode of GR/PDDA/GCE. The composite material was characterized by FTIR, showing that the synthesis come out all right. The electrochemical features of the composite modified electrode were studied by CV, demonstrating that coating of GR/PDDA on GCE not only increased the surface area of the modified electrode but also accelerated the speed of transference of electric charges. Furthermore, electrochemical behaviors of nimodipine (NM) and nifedipine (NF), at the composite modified electrode were studied in buffer solution of dissodium hydrogen phosphate and citric acid at pH 6.0. It was found that sensitive reduction peaks at -0.444 V (for NM) and at -0.737 V (for NF) were observed and linear relationships between values of reduction peak current and concentration of NM and NF were obtained in the ranges of 1.0×10^-6 to 1.4×10^-4mol·L^-1 and 4.0×10^-7 to 2.6×10^-4mol·L^-1 respectively. Detection limits (3s) found were 3.9×10^-7mol·L^-1 (for NM) and 5.6×10^-8mol·L^-1 (for NF). Simultaneous CV determination of NM and NF (2 commonly used drugs for blood vessel diseases) in human serum samples was shown to be feasible.