As an oral nonsteroidal antiestrogen drug, tamoxifen (TMX) has been widely utilized for the prevention and treatment of breast cancer. In the current research, using differential-pulse voltammetry (DPV), an electrochemical investigation of the interaction between TMX and salmon-sperm double-stranded DNA (ds-DNA) was conducted with a graphene paste electrode (GPE). To determine TMX, a simple and sensitive biosensor was fabricated through this interaction. A linear dynamic range between 8.0 x 10(-7) and 8.5 x 10(-5) M was exhibited by DPV for TMX. Finally this modified electrode was used for determination of TMX in TMX tablet, serum and urine samples. (C) 2017 The Electrochemical Society. All rights reserved.