BackgroundMaintained abstinence during the first 24 h of a quit attempt is a critical predictor of long-term smoking cessation. Little is known about sex differences in the very early abstinence period, particularly in the context of low- and middle-income countries (LMICs) with varying anti-smoking policies and female smoking prevalences. We examined female sex effects on one-day relapse in a cross-national sample from 12 LMICs. MethodsData from the Global Adult Tobacco Survey (2008–2012) included nationally representative samples from 12 LMICs restricted to smokers with ≥ 1 quit attempt in the past 12 months (n = 16,576). We ran adjusted logistic regression models for female sex effects on one-day relapse, adjusting for nine individual-level demographics (e.g., age, education, age at smoking initiation) and smoking cessation variables (e.g., exposure to health warnings, receipt of counseling). We then conducted a meta-analysis adjusted for national-level and policy measures through meta-regression (e.g., cigarette consumption per capita, percent of cigarette box covered with warning labels). ResultsOne-day relapse prevalence varied across countries (2.7–13.6%). The odds of one-day relapse were significantly higher for women than for men in six countries (adjusted for nine individual-level sociodemographic variables), and there were no significant sex differences in the remaining six countries. Result remained significant after meta-regressions for national-level tobacco consumption and policy measures. Sensitivity analyses showed that the odds of one-day relapse for women remained significant when excluding countries with both higher and lower relative rates of female smoking. Larger warning labels on cigarette packs were associated with reduced odds of one-day relapse among women. ConclusionThe first day of a quit attempt is more challenging for women than men in LMICs. Tailored interventions incorporating national policies, in addition to counseling and pharmacotherapy, could play an essential role in supporting women during the initial abstinence phase of smoking cessation in LMICs.