Background Several experimental studies have suggested beneficial effects of Ceriporia lacerata on glucose metabolism. However, there has been no human study assessing the effects of C. lacerata on glucose metabolism. Therefore, we investigated whether C. lacerata improves glucose control and insulin resistance in type 2 diabetes patients. Methods Ninety patients diagnosed with type 2 diabetes (T2DM) for more than 6 months were enrolled. Subjects were randomly divided into placebo (n = 45) or C. lacerata (n = 45) groups and then assigned to take placebo or C. lacerata capsules (500 mg/capsule) for a 12-week intervention period. Biochemical markers, including fasting glucose, 2-hour postprandial plasma glucose, and lipid profile levels, as well as insulin, c-peptide, and Hba1c, were measured. Furthermore, insulin sensitivity indices, such as HOMA-IR, HOMA-beta, and QUICKI, were assessed before and after the 12-week administration. Results Eighty-four patients completed the study. There were no significant differences in fasting, postprandial glucose, HbA1c, or lipid parameters. HOMA-IR and QUICKI indices were improved at week 12 in the C. lacerata group, especially in subjects with HOMA-IR of 1.8 or more (p < 0.05). Fasting, postprandial c-peptide, and insulin levels decreased at week 12 in the C. lacerata group (p < 0.05). These significant differences were not observed in the placebo group. Conclusion Twelve-week administration of C. lacerata in T2DM patients resulted in significant improvement in insulin resistance, especially in those with lower insulin sensitivity. A larger population study with a longer follow-up period and an effort to elucidate the mechanism is warranted to further assess the effects of C. lacerata on T2DM patients.