Pregnant women with substance use disorder (SUD) comprise an underserved population with complex treatment needs, including complications from trauma histories and comorbid psychological disorders. Using ecological momentary assessment, we examined momentary fluctuations in posttraumatic stress disorder (PTSD) symptoms, prenatal bonding, and substance craving, among pregnant women in SUD treatment who had a history of trauma. We hypothesized that (a) PTSD symptoms and prenatal bonding would each be associated with substance craving and (b) PTSD symptoms would be negatively associated with prenatal bonding, and this would at least partially account for the association between PTSD symptoms and substance craving (i.e., indirect effect). Participants (n = 32) were on average 27.1 weeks pregnant (SD = 5.27), 27.8 years old (SD = 4.54), and predominantly Hispanic/Latina (66%). At the within subjects level, higher momentary ratings of PTSD symptoms were associated with lower quality (but not intensity of preoccupation) of prenatal bonding, which in turn was associated with greater craving. Lower quality of prenatal bonding partially mediated the positive association between PTSD symptoms and craving, which remained strong after accounting for prenatal bonding. Our results provide some preliminary support for considering interventions aimed at stabilizing or decreasing PTSD symptoms and stabilizing or increasing prenatal bonding to reduce substance craving and, thus, the risk of perinatal substance use among women with SUD and trauma histories. (PsycINFO Database Record (c) 2020 APA, all rights reserved).