ABSTRACT Background: To investigate relationships between microsatellite instability (MSI) and the clinicopathological characteristics of colorectal cancer (CRC) to facilitate the provision of targeted therapy and immunotherapy for CRC related to MSI, and provide a basis for better prognoses. Materials and Methods: Data were obtained from the information system of the Pathology Department of the Fourth Affiliated Hospital of Harbin Medical University, China, from January 01, 2021 to September 30, 2022. Clinicopathological information, including sex, age, tumor size, and associated expression of MSI, was collected. Results: CRC associated with MSI usually occurred in people aged over 50 years. It was related to tumor diameter, which was 5–10 cm at the most. Most tumors occurred in the right colon and were moderately to poorly differentiated. PCR detected 29 patients, including 24 cases of microsatellite stable (MSS), one case of MSI-low, and four cases of MSI-high. The expression of mismatch repair (MMR) protein in these 29 patients was also investigated via immunohistochemistry (IHC), which detected 25 cases of MSS and four cases of MSI-high. The consistency between IHC and PCR was 96.6%. Conclusion: The expression of MMR is related to age, tumor diameter, tumor location, and tumor differentiation. It was not related to gender, lymphovascular and perineural invasion, lymph node metastasis, TNM stage, or P53 expression. The consistency between IHC and PCR was 96.6%.