Effect of miR-21 and miR-138 on the proliferation of colon cancer cells and their association with prognosis were investigated. Expression levels of miR-21 and miR-138 in colorectal cancer and normal adjacent tissues were compared. Differential expression of miR-21 and miR-138 in colon cancer tissues with different clinicopathological features were analyzed. miR-21 and miR-138 expression vectors were established and transfected into cells of colon cancer cell line SW480. Methyl thiazolyl tetrazolium (MTT) assay was used to detect the proliferation of SW480 cells. Kaplan-Meier method and log-rank test were used to study the relationship between miR-21 and miR-138 expression and prognosis. Cox proportional hazards model was used to analyze the factors related to prognosis of colon cancer. Expression level of miR-21 in colon cancer tissues was significantly higher than that in adjacent tissues, and expression level of miR-138 was lower in cancer tissues than in adjacent tissues (P<0.001). Expression of miR-21 and miR-138 was associated with the degree of differentiation, lymph node metastasis, distant metastasis, and TNM stage (P<0.05). miR-21 promotes proliferation of colon cancer cell line SW480, and miR-138 inhibits cell proliferation. Survival analysis showed that the survival time of patients with high expression of miR-21 was significantly shorter than that of patients with low expression of miR-21, while survival time of patients with high expression of miR-138 was significantly longer than that of patients with low expression of miR-138 (log-rank, P<0.05). miR-21 is highly expressed in colon cancer tissues and is positively associated with the degree of malignancy of patients but negatively associated with survival. miR-138 expression is low in colon cancer tissues and is negatively associated with the degree of malignancy of patients but positively associated with survival. miR-21 and miR-138 may be involved in the regulation of colon cancer cell proliferation.