Objective    To investigate the correlation between the expression of nucleostemin (NS) and proliferating cell nuclear antigen (PCNA) in colorectal cancer tissues and serum folic acid concentrations.     Methods    From March to December 2009

colorectal cancer tissues were collected from 50 patients through colonoscopy. According to international colorectal cancer classification standard for the pathological

which divided into well-differentiated group(n=12)

moderately differentiated (n=17)

poorly differentiated(n=21)and corresponding normal intestinal mucosa tissues. At the same time

venous blood of 5 ml was collected from each of the above patients. Immunohistochemistry was used to detect the expression of NS and PCNA in colorectal cancer tissues and normal intestinal mucosa tissues. Serum folic acid concentrations were determined with magnetic chemiluminescence immunoassay.     Results    The positive expression rates of NS and PCNA in colorectal cancer tissues were 70% (35/50) and 72% (36/50)

while neither of NS and PCNA expression was detected in the normal intestinal mucosa tissues. The positive expression rates of NS and PCNA in well differentiated colorectal cancer tissues were 41.7% (5/12) and 33.3% (4/12)

which were significantly lower than those [76.5%(13/17) and 82.4%（14/17）] in the  moderately differentiated colorectal cancer tissues and [81.0% (17/21) and 85.7% (18/21)] in the poorly differentiated colorectal cancer tissues (P0.05). There was no significant difference in serum folic acid concentration between NS and PCNA positive expression group and negative expression group (P0.05).     Conclusion    NS and PCNA are expressed in colorectal cancer tissues

and their expression levels are correlated with the malignant degree of colorectal cancer. Serum folic acid concentration is not related to NS and PCNA expression in colorectal cancer.