Abstract: An ultrasensitive electrochemical immunosensor modified with graphene and dienestrol(DE)was developed for the detection of dienestrol through indirect competition with K₃Fe(CN)₆ acting as the redox probes. The results revealed that under optimized conditions a calibration for DE was obtained with a linear range of 500-5 000 ng/mL and the detection limit was up to 0. 2 ng/mL, showing that the proposed electrochemical immunosensor had excellent sensitivity and wide detection range. The immunosensor was examined in real samples for the analysis of DE. A good recovery in the range of 83. 8%-97. 7% was obtained in pork samples.