Objective To evaluate branched-chain DNA (b-DNA) signal amplification and semi-quantitative (Sq) RT-PCR in detection of free cancer cells in peritoneal flushing fluid of colorectal cancer patients during surgery. Methods The CEA mRNA in peritoneal flushing fluid in 48 cases of colorectal cancer were detected by b-DNA and SqRT-PCR. Peritoneal flushing fluid cytology (PLC) was conformed simultaneously to detect the free cancer cells. The peritoneal flushing fluid of 12 cases with colorectal benign disease were taken as negative control, GAPDH mRNA as internal control. Results In colorectal cancer patients, positive rate of free cancer cells by bDNA and SqRT-PCR （43.8%, 31.3%） was higher than that by PLC （4.2%）. The relative quantitative expressions of CEA mRNA were related to the Dukes staging， depth invasion and differentiation degree (Plt;0.05)， but irrelevant to tumor size，the patients’ age and gender (Pgt;0.05).Conclusion Both b-DNA and SqRT-PCR technologies have advantages and disadvantages to detect free cancer cells in peritoneal flushing fluid， which are related to clinicopathological factors.