OBJECTIVE: Depression among pregnant women is a prevalent public health problem associated with poor maternal and offspring development. Behavioral activation (BA) is a scalable intervention aligned with pregnant women's preference for nonpharmacological depression care. This is the first test of the effectiveness of BA for depression among pregnant women, which aimed to evaluate the effectiveness of BA as compared with treatment as usual (TAU). METHOD: Pregnant women (mean age = 28.75 years; SD = 5.67) with depression symptoms were randomly assigned to BA (n = 86) or TAU (n = 77). Exclusion criteria included known bipolar or psychotic disorder or immediate self-harm risk. Follow-up assessment occurred 5 and 10 weeks postrandomization and 3 months postpartum using self-report measures of primary and secondary outcomes and putative targets. RESULTS: Compared with TAU, BA was associated with significantly lower depressive symptoms (d = 0.34, p = .04) and higher remission (56.3% vs. 30.3%, p = .003). BA also demonstrated significant advantage on anxiety and perceived stress. Participants attended most BA sessions and reported high satisfaction. Participants in BA reported significantly higher levels of activation (d = 0.69, p < .0002) and environmental reward (d = 0.54, p < .003) than those who received TAU, and early change in both of these putative targets significantly mediated subsequent depression outcomes. CONCLUSIONS: BA is effective for pregnant women, offering significant depression, anxiety, and stress benefits, with mediation analyses supporting the importance of putative targets of activation and environmental reward. (PsycINFO Database Record