We are just beginning to understand how microRNAs (miRNAs) are involved in tumor-related processes in humans. Applying real-time RT-PCR, we investigated the miR-31, miR-143 and miR-145 expression in 98 primary CRC specimens, along with the corresponding normal mucosa specimens, and analyze the relationship of their expression with clinicopathological features. Our results showed the miR-31 expression was up-regulated in CRC compared to normal mucosa (p = 0.001). Furthermore, miR-31 expression was positively related to advanced TNM stage (p = 0.026) and deeper invasion of tumors (p = 0.024). MiR-145 was down-regulated in both colon (p = 0.001) and rectal (p = 0.012) cancer. MiR-143 was only down-regulated in colon cancer (p = 0.023) but not in rectal cancer (p = 0.351). There was no relationship of miR-143 and miR-145 expression with other clinicopathological features (p > 0.05), except that the miR-145 expression was related to cancer site (p = 0.03). In conclusion, the miR-31 overexpression may be involved in the development and progression of CRC. The miR-143 and miR-145 may play a certain role in the development of colon and/or rectal cancers but not in progression of the disease.