In this work, we have developed for the first time a carboxylic group riched graphene oxide based disposable electrochemical immunosensor for cancer biomarker detection using methylene blue (MB). The developed immunosensor is highly sensitive for detection of biomarker Mucin1 (MUC1) in human serum samples. Development of this disposable electrochemical immunosensor was premeditated by applying specific monoclonal antibodies against MUC1. In this method, we explored highly conductive surface of carboxylic group (-COOH-) rich graphene oxide (GO) on screen-printed carbon electrodes (SPCE). This modified GO-COOH-SPCE was employed for the detection of MUC1 protein based on the reaction with methylene blue (MB) redox probe using differential pulse voltammetry (DPV) technique. Developed immunosensor exhibited good detection range for MUC1 with excellent linearity (0.1 U/mL- 2 U/mL), with a limit of detection of 0.04 U/mL. Upon potential application of developed biosensor, good recoveries were recorded in the range of 96–96.67% with % R.S.D 4.2. Analytical performance of the developed immunosensor assures the applicability in clinical diagnostic applications. © 2018 Elsevier Inc.