Background: Ecological momentary assessments (EMA) are data collection approaches that characterize behaviors in real-time. However, EMA is underutilized in alcohol and substance use research among men who have sex with men (MSM). The aim of this analysis is to explore the correlates of engagement in EMA text messages among substance-using MSM in San Francisco. Methods: The present analysis uses data collected from the Project iN pilot study (n = 30). Over a two-month period, participants received and responded to EMA daily text messages inquiring about their study medication, alcohol, and methamphetamine use. Baseline characteristics including demographics, alcohol use, and substance use were examined as potential correlates of engagement in EMA text messages in logistic regression and proportional hazards models. Results: Participants had a 74% response rate to EMA text messages over the study period. MSM of color had significantly lower adjusted odds of responding to EMA texts 80% of the time or more, compared to white MSM (adjusted odds ratio = 0.05, 95%CI = 0.01-0.38). College-educated MSM had a lower adjusted hazard of week-long discontinuation in EMA texts (adjusted hazard ratio = 0.12, 95%Cl = 0.02-0.63). Older MSM had a higher adjusted hazard of week-long discontinuation in EMA texts (adjusted hazard ratio = 1.15, 95%CI = 1.01-131). Conclusion: Differences in engagement in EMA text prompts were discovered for MSM with different racial/ ethnic backgrounds, ages, and education levels. Substance use variables were not correlated with engagement in text messages, suggesting that EMA may be a useful research tool among actively substance-using MSM in San Francisco. Published by Elsevier Inc.