Abstract: Background: Nearly 2 million U.S. veterans live with co-occurring alcohol use disorder and posttraumatic stress disorder (AUD/PTSD). Extant AUD/PTSD treatments emphasize symptom reduction, sometimes overlooking psychosocial functioning improvements, and have dropout rates as high as 50 %. Additionally, current approaches to measuring psychosocial functioning are limited to self-report. This study protocol describes a 1:1 parallel, two-arm, pilot randomized controlled trial comparing Behavioral Activation (BA) psychotherapy to Relapse Prevention (RP) psychotherapy for veterans with AUD/PTSD. Methods: Forty-six veterans with AUD/PTSD will be block-randomized to eight weekly, virtual, hour-long individual sessions of BA or RP. Clinical interview, self-report, and geospatial assessments will be administered at pre- and post-treatment. Select outcome and exploratory measures will be administered during treatment. Analyses will focus on trial feasibility, BA acceptability, and preliminary efficacy. Geospatial analyses will explore whether pre- to post-treatment changes in geospatial movement can be used to objectively measure treatment response. The study site and an independent Data and Safety Monitoring Board will monitor trial progress, safety, and quality. De-identified data from consenting participants will be submitted to a sponsor-designated data repository. Conclusion: If successful, this trial could help to provide veterans with AUD/PTSD with a more acceptable treatment option. Positive findings would also lay groundwork for testing BA in civilians with AUD/PTSD. Finally, by incorporating novel geospatial methods and technologies, this study could potentially yield a new approach to objectively measuring AUD/PTSD recovery that could be used in other clinical trials.