Sexual minority women (SMW) evidence elevated rates of trauma exposure, posttraumatic stress (PTS), and alcohol consumption. Self-medication models of drinking suggest that individuals may drink to cope with symptoms of PTS, but this possibility remains untested among SMW. The current study used data from drinking days collected via daily diary assessments from 81 trauma-exposed SMW. Participants were mostly White (72.8%) and ranged in age from 18 to 25 ( = 23.8). Participants were followed over 2 14-consecutive-day measurement bursts (720 person-days reported). Analyses were conducted to examine whether coping drinking motives (vs. social, enhancement, and conformity drinking motives), as assessed by an adapted Drinking Motives Questionnaire, mediated the daily level relationship between PTS symptoms (assessed by the PTSD Checklist) and the number of standard drinks per drinking day. Results from multilevel structural equation models indicated that day-to-day fluctuations in PTS symptoms, as well as average levels of PTS symptoms, were associated with increased coping drinking motives. Coping drinking motives, but not other drinking motives, mediated within-person associations between PTS and drinking, such that daily fluctuations in PTS symptoms were associated with stronger-than-normal coping drinking motives, which in turn predicted more drinks per drinking day. Results highlight the importance of coping drinking motives and suggest that alternative coping strategies may help trauma-exposed SMW to manage heightened PTS symptoms without increasing their alcohol consumption. (PsycInfo Database Record (c) 2021 APA, all rights reserved).