John Cunningham virus (JCV) is a type of human polyomavirus. It s widespread virus detected in different population throughout the word. JCV encodes for T-Ag which have oncogenic capability through bind and inactivate tumor suppressor protein p53 and pRband can interfere with cell cycle control and genomic instability mechanisms. The association between JCV and colorectal carcinoma still awaits the final conformation. Determine the role of JCV in malignant transformation of colorectal carcinoma and to study the interaction of JC viral TAg and estimation the possible interaction of T-Ag with B-catenin. involved the use of 28 colonic tissue biopsies taken through colonoscopy from patients with colorectal cancer and 31 tissue biopsies from patients without CRC attended to GIT Endoscopic Unite of Oncology Hospital, Baghdad Teaching Hospital, and Al- Yarmouk Teaching Hospital during the period from June 2013 to march 2014. JCV T Ag was detected by real time PCR and by in situe hybridization, Viral DNA load of positive samples were determined by quantitative real-time PCR.B-catenin was detected by out of 28 CRC cases, 16(57.1%) were positive for T-Ag compared to 9/33(27.3%) in non CRC patient (p=0.018), 12/28(42.9%) of CRC cases were positive for agnoprotein gene compared to 5/33(15.2%) in non CRC patient (p=0.016). Nuclear localization of B-catenin was detected in 12/28(42.86%) of CRC groups, while none of the control group revealed positive nuclear staining (p<0.05). No significant associations found neither to grades nor to the site of tumor. Colorectal carcinomas contain more viral copie and express JCV T-Ag and agnoprotein genes compared to normal colonic tissues.