Colorectal cancer (CRC), also known as colon cancer, rectal cancer, or colon cancer is one of the important mortal cancers of the gastrointestinal tract in Iran and worldwide. Interleukin 18 is one of the cytokines that causes inflammation and plays a real role in the inhibition of CRC development and evaluation of its rate is significant in cancer patients. The purpose of the present study was to investigate the IL-18 gene expression and its serum levels in Iranian CRC patients compared to healthy people. A total of 35 serum samples and 24 complete blood cells (CBCs) from CRC patients and as well as 20 control samples (healthy people) were collected from Al-Zahra hospital (Isfahan city, Iran) and serum and RNA specimens were isolated for molecular and serological investigations. The expression level of IL-18 gene and its serum level for comparison in both CRC patients and healthy people groups were evaluated by quantitative real-time reverse transcription PCR (q-RT-PCR) technique and ELISA assay. The comparison of IL-18 gene expression and its serum level in blood of the CRC patients and healthy people using realtime PCR and ELISA techniques were showed that this cytokine level was increased significantly in cancer patients (p < 0.05). According to the significant role of IL-18 as a pro-inflammatory cytokine in developing inflammation of gastrointestinal tract and cancer and increasing of this cytokine expression in the results of our research in CRC patients compared to the control subjects, for diagnosing or pre-screen of CRC and other cancer patients, it would be better IL-18 expression level is check in laboratories.