Medication for opioid use disorder (MOUD) is evidence-based treatment during pregnancy and postpartum. Prior studies show racial/ethnic differences in receipt of MOUD during pregnancy. Fewer studies have examined racial/ethnic differences in MOUD receipt and duration during the first year postpartum and in the type of MOUD received during pregnancy and postpartum. We used Medicaid administrative data from 6 states to compare the percentage of women with any MOUD and the average proportion of days covered (PDC) with MOUD, overall and by type of MOUD, during pregnancy and four postpartum periods (1-90 days, 91-180 days, 181-270 days, and 271-360 days postpartum) among White non-Hispanic, Black non-Hispanic, and Hispanic women diagnosed with OUD. White non-Hispanic women were more likely to receive any MOUD during pregnancy and all postpartum periods compared to Hispanic and Black non-Hispanic women. For all MOUD types combined and for buprenorphine, White non-Hispanic women had the highest average PDC during pregnancy and each postpartum period, followed by Hispanic women and Black non-Hispanic women (e.g., for all MOUD types, 0.49 vs. 0.41 vs. 0.23 PDC, respectively, during days 1-90 postpartum). For methadone, White non-Hispanic and Hispanic women had similar average PDC during pregnancy and postpartum, and Black non-Hispanic women had substantially lower PDC. There are stark racial/ethnic differences in MOUD during pregnancy and the first year postpartum. Reducing these inequities is critical to improving health outcomes among pregnant and postpartum women with OUD.