Oral cancer (OC) is considered as sixth most common cancer in the world. The challenge facing oral cancer is the lack of non-invasive, rapid, sensitive, accurate, and inexpensive screening and diagnosis methods. Given the increasing importance of prevention, prognosis, and early-stage diagnosis of cancer in improving of survival rate, the use of efficient diagnostic devices is essential. In this study, novel bioassay based on antigen and antibody immunocomplex was proposed for early stage diagnosis of OC. For the first time, an efficient immunosensor (Cys-GA-anti-Cyfra21.1-BSA-Cyfra21.1 antigen/AuE) was successfully designed and developed to the detection and determination of the Cyfra21.1 biomarker in unprocessed human saliva samples. The Au electrode was modified by Cysteamine (CysA) and Glutaraldehyde (GA) respectively via self-assembly as a substrate to immobilize the biological agents. The engineered immunosensor exhibit an excellent ability to detect and determine of Cyfra21.1 biomarker in low concentrations in unprocessed human saliva samples. Under the optimized operating conditions, the results demonstrate that the desired platform has a good sensitivity in the detecting of Cyfra21.1 with the low limit of quantitation (LLOQ) of 2.5 ng/mL, which this evaluation was performed at a wide linear range of 2.5−50 ng/mL. The use of the CysA-GA nano-hybrid as extraordinary stable substrate and extensive platform to place recognition elements was investigated using various electrochemical methods including cyclic voltammetry (CV) and square wave voltammetry (SWV). In this study, the engineered biosensor was used to non-invasive detection of Cyfra21.1 in unprocessed human saliva sample. Based on results, CysA-GA-anti-Cyfra21.1 antibody-BSA- Cyfra21.1 antigen/AuE with significantly high current intensity can provide appropriate, reliable, affordable, quick, and user-friendly diagnostic device to monitoring oral abnormality by detection and determination of Cyfra21.1 biomarker in human real sample. Above all, the easy to prepared designed immunosensor can be an extremely promising candidate to specific and favorable for a vast range of clinical diagnosis of OC in near future.