Higher cancer mortality rate can be prevented by the early detection of cancer-associated biomarkers and appropriate therapeutic intervention. Recently, electrochemical biosensors have drawn a great deal of interest because of their extremely high sensitivity, selectivity, and affordability in early cancer detection. Herein, we fabricated an aptasensor for the inexpensive and label-free detection of the epidermal growth factor receptor (EGFR) antigen, a biomarker linked to breast cancer. The reduced graphene oxide-yttrium nanocomposite was synthesized and characterized using FTIR, XRD, TEM, SEM, Raman spectroscopy, and UV-vis spectroscopy, which confirmed the synthesis of the nanocomposite. The synthesized material was used for the fabrication of electrochemical aptasensor for the detection of epidermal growth factor receptor antigen. The developed sensor (Y2O3-rGO/Apt/BSA) showed a wide linear detection range (10 fg mL(-1) to 100 ng mL(-1)), a low detection limit of 0.251 fg mL(-1), and an excellent sensitivity of 51.96 mu A fM(-1) center dot cm(-2). The aptasensor also provides a straightforward and quick approach to EGFR antigen detection in biological serum samples. The simple and facile synthesis method reported in this work led to the production of a high-purity, water-dispersible yttrium functionalized reduced graphene oxide nanocomposite for cost-effective, faster, and ultrasensitive detection of breast cancer biomarkers using electrochemical aptasensors.