Maternal psychosocial stress is associated with delivery of both small- and large-for-gestational-age newborns. Prior studies have relied on methods that do not capture fat mass (FM) vs. fat-free mass (FFM). We aimed to assess the relationship of maternal psychosocial stress, using the Edinburgh Postnatal Depression Scale (EPDS) and Cohen’s Perceived Stress Scale (PSS), with newborn body composition. The sample included 604 mother/newborn pairs in the Healthy Start study. We used linear regression to examine associations of EPDS (>6.5 vs. ≤6.5) and PSS (>21 vs. ≤21) with newborn adiposity (FM and %FM measured by air displacement plethysmography [ADP], BMI-for-age, weight-for-length, and weight-for-age z-scores) and lean mass (FFM and length-for-age z-score). Average age of the women was 29.2 ± 6 y. Fifty-five percent of the women were white, 26.2% Hispanic, and 12.1% Black. Twenty-four percent of women had EPDS >6.5 and 18.1% had PSS >21. Mean ± SD birthweight was 3136 ± 437 g. After adjustment for confounders, EPDS >6.5 vs. ≤6.5 corresponded with 35.3 (95% CI: 6.6, 64.0) g lower offspring FM and 0.18 (−0.03, 0.39) units shorter length z-score. PSS was not associated with any neonatal outcomes. Maternal psychosocial stress is associated with delivery of shorter newborns with less FM.