Preventive services can help reduce costs associated with chronic conditions. Medicaid beneficiaries have high rates of chronic conditions, but state Medicaid coverage and cost-sharing of preventive services varies widely. States that chose to expand Medicaid under the ACA were incentivized to cover recommended preventive services at no cost-sharing. This study evaluates whether state Medicaid policy and Medicaid expansion were associated with overall utilization, and disparities in utilization of preventive services among vulnerable populations.We used Medicaid policy data from Kaiser Family Foundation and MEPS data (2009–2014, n = 15,610), collected and analyzed in 2017. We used multivariable logistic regression, difference-in-differences, and difference-in-difference-in-differences models to examine the association between state Medicaid preventive service policy and Medicaid expansion on overall utilization, and disparities in utilization among race/ethnicity and income groups for blood pressure check, cholesterol screening, and flu shot.Medicaid coverage of flu shot was significantly associated with utilization (p < 0.001). Medicaid expansion significantly increased flu shot utilization among near-poor individuals (p < 0.01), Asians, and Latinos and blood pressure screening among African Americans (p < 0.05).For flu shot, the ACA is reaching its target audience: those in the coverage gap between Medicaid and private insurance. Increasing access to preventive services may not be enough to increase utilization, especially for vulnerable populations and/or the previously uninsured. Focusing on provider adherence to preventive service guidelines and education around who is eligible for what service and when could help increase utilization of preventive services in the future.