Midlife women are vulnerable to developing obesity. Behavioral and psychosocial factors including sleep duration, stress eating, and negative emotionality are risk factors. However, little is known about the complex daily interplay between sleep, eating, emotion, and weight among midlife women. The current study examined how daily sleep, using food to cope, and negative emotionality are associated with weight using a daily process research design. An archival analysis was performed using the Midlife in the United States-II study (MIDUS II). The sample consisted of 489 midlife women (40–64 years of age). Variables included ecological momentary assessments of daily sleep duration, using food to cope, and negative affect (means and intraindividual variability) and a standardized measurement of BMI. Sleep duration variability was a significant predictor of BMI, albeit the model only accounted for .8% of the variance in BMI (b = .019, p < .05). In the final adjusted model, sleep duration variability, using food to cope, age, and physical activity were all significant predictors of BMI F(5, 559) = 21.503, p < .001, R2 = .161, ⨂R2 = .024, p = .001. Variability in negative affect, mean sleep duration or negative affect and the interactions between sleep duration (mean, variability) and negative affect (mean, variability) were not significant. Greater variability in sleep duration and greater use of food to cope predicted higher BMI in this sample across age and physical activity levels. Results highlight that daily health and psychosocial factors play an important role in weight.