PURPOSE: To determine components of excess preterm birth (PTB) rates for U.S.-born black women relative to both foreign-born black women and U.S.-born white women attributable to differences in observed sociodemographic, behavioral, and medical risk factors. METHODS: Using the 2013 U.S. natality files, we used Oaxaca-Blinder decomposition on the absolute scale to estimate the contribution of the group differences in the prevalence of PTB predictors between U.S.- and foreign-born black women and U.S.-born black and U.S.-born white women. RESULTS: U.S.-born blacks had a 3.2 (95% confidence interval: 3.0-3.5) and 4.4 (95% confidence interval: 4.3-4.5) percentage point higher risk of PTB than foreign-born blacks and U.S.-born whites, respectively. The variables in the models explained between 18% and 27% of the PTB disparities. Differences in paternal acknowledgment (about 12%), maternal hypertension (about 7%-11%), and maternal education (about 6%-10%) explained the largest proportion of these disparities. CONCLUSIONS: Programs and policies that address both distal and proximate factors, including the social determinants of health and the prevention and management of hypertension, may reduce the higher rates of PTB among U.S.-born black women compared to foreign-born black women and U.S.-born white women.