Abstract: Objective To study the expression of NPAS2 in colorectal cancer (CRC) and analyze its relationship with the clinicopathological parameters and prognosis of the patients. Methods Real-time q-PCR was used to detect the expression of NPAS2 mRNA in 40 fresh CRC tissues and paired adjacent tissues; immunohistochemistry was used to detect the expression of NPAS2 protein in 120 paraffin-embedded tumor and adjacent tissues. The relationship between NPAS2 expression level and the 5-year survival rate of 78 CRC patients with follow-up data were analyzed with Kaplan-Meier survival analysis. Results Compared with the adjacent tissues, fresh CRC tissue expressed significantly lower NPAS2 mRNA levels (P<0.01). Among the paraffin-embedded CRC tissues, 19.2% were positive for NPAS2 expression, as compared to a much higher rate of 62.5% in the adjacent tissues (P<0.05). The expression of NPAS2 was correlated with the tumor size, lymph node metastasis and TNM stages (P<0.05) but not with the patients’ gender, age, distant tumor metastasis, differentiation, or invasion. Patients with high NPAS2 expression levels had a significantly higher 5-year survival rate than those with low NPAS2 expressions (P=0.0001). Conclusion NPAS2 is down-regulated in CRC and closely correlated with the malignant biological behavior of the tumor and 5-year survival of the patients, suggesting its value in predicting the prognosis of the CRC patients.