Early colorectal cancer (CRC) diagnosis improves disease prognosis and treatment. However, current approaches are suboptimal, and no serum-based test is sufficient for widespread use. This study evaluated serum P53 protein efficacy as a non-invasive CRC marker. Using western blotting and ELISA, the serum P53 protein level was evaluated in 237 participants (127 CRC and 70 benign disorder patients, and 40 healthy controls). The area under the receiver operating characteristic curve (AUC) was applied for evaluating diagnostic performance. An immunoreactive band at 53-KDa was detected corresponding to serum P53 protein in only patients with colorectal diseases. Aberrant P53 both detection rates and optical density level in patients with CRC (69.3%; 1.19±0.03) were significantly (P=0.001) higher than in patients with non-malignant benign growth (27.1%; 0.51±0.02). Serum P53 protein effectively-identified CRC (AUC=0.90, 87.0% sensitivity, and 76.4% specificity) from all noncancerous individuals and tumor early stages (AUC=0.84, 85.5% sensitivity, and 72.9% specificity) from benign disorders. Elevated detection rates and optical density levels were significantly associated with advanced tumor stages (P=0.015), high grades (P=0.001), lymph node invasion (P=0.010), and distant metastasis (P=0.001). In conclusion, serum P53 protein could be an effective CRC biomarker especially for differentiating early disease stages from benign disorders