Purpose: This study examined change in healthcare utilization by disease severity after case management (CM) for Medicaid. Methods: Data were extracted from survey data on "Healthcare utilization and health status of Medicaid beneficiaries" conducted in 2007 and 2008 by the Ministry for Health, Welfare and Family Affairs. This study was designed to compare change in healthcare utilization between the CM group and the non-CM group. The subjects were 528 Type I Medicaid beneficiaries who utilized healthcare more than 365 days during 2006. Results: In beneficiaries having fewer than 3 among the 11 notified diseases, the CM group showed a significantly larger decrease in outpatient day, outpatient expense, medication day, and medication expense than the non-CM group. In beneficiaries having 3 or more among the 11 notified diseases, however, there was no significant difference in healthcare utilization between the CM group and the non-CM group. Conclusion: CM worked effectively on Medicaid beneficiaries outpatient healthcare utilization for mild diseases. However, its effects on hospitalization, which is a major cause increasing the total expense, were not observed. Therefore, a future study is needed to develope strategies to reduce hospitalization and care for Medicaid beneficiaries with severe diseases.