Colorectal cancer is still a major global health concern, and early detection and accurate biomarker analyses are critical to its successful management. This paper describes the design and testing of a new biosensor based on a graphene oxide (GO) nanocomposite for the exact measurement of carcinoembryonic antigen (CEA), a well-known biomarker for colorectal cancer. The current study attempted to create a highly sensitive immunosensor for sensitive measurement of CEA based on a polypropylene-imine-dendrimer (PPI) and GO nanocomposite on GCE (PPI/GO/GCE). The PPI/GO nanocomposite served as an appropriate biocompatible nanostructure with a large surface area for immobilizing carcinoembryonic antigen (anti-CEA) and bovine serum albumin (BSA) molecules (BSA/anti-CEA/PPI/GO/GCE), thereby promoting the selectivity of electrochemical immunosensors, according to structural and electrochemical studies. Results showed that the BSA/anti-CEA/PPI/GO/GCE as a selective, sensitive, and stable immunosensor revealed a wide linear response from 0.001 to 2000 ng/mL, and a limit of detection of 0.3 pg/mL, which indicated comparable or better performance towards the CEA immunosensors in recent reports in the literature. This was due to the synergetic effect of the GO nanosheets and PPI with porous structure and more conductivity. Analytical results showed values of RSD (4.49%-5.04%) and recovery (90.00%-99.98%) are suitable for effective and accurate practical assessments in CEA in clinical samples. The capacity of the BSA/anti-CEA/PPI/GO/GCE to determine CEA in human blood was studied.