Abstract Introduction Sexual interest/arousal disorder (SIAD) includes persistent and distressing symptoms of low sexual desire and/or arousal, which are the most common sexual difficulties among women. Meta-analyses of randomized clinical trials show that psychological therapies produce moderate to large improvements in clinically low sexual desire (Banbury et al., 2021; Frühauf et al., 2013; Günzler & Berner, 2012). However, these therapies focus on individuals, neglecting the partner’s experience, which is known to affect and be affected by SIAD symptoms (Rosen et al., 2019). Despite the prevalence of SIAD and importance of interpersonal factors in the development and maintenance of low sexual desire, there are no empirically supported couple-based sex therapy interventions for this disorder. Objective To develop a new couple-based sex therapy intervention for SIAD following a cognitive-behavioral couple therapy (CBCT) framework. To test the CBCT intervention for SIAD in terms of feasibility, acceptability, and preliminary efficacy. Methods Nineteen couples in which a woman was diagnosed with SIAD completed a 16-session CBCT intervention delivered via Zoom by therapists with PhD-level training in clinical psychology. The goals of the CBCT intervention were to re-conceptualize SIAD in biopsychosocial-interpersonal terms, modify psychological and interpersonal factors associated with low sexual desire/arousal (Rosen & Bergeron, 2019), and consolidate skills. Participants completed measures of dyadic sexual desire and sexual distress (primary outcomes) as well as sexual communication, sexual satisfaction, relationship intimacy, and relationship satisfaction (secondary outcomes) at pre-treatment, post-treatment, and at 6-month follow-up. We assessed preliminary efficacy using multilevel models guided by the actor-partner interdependence model (Kenny et al., 2020) to account for the interdependence of couple members’ data. Results The CBCT intervention was feasible as indicated by therapists’ high adherence to the treatment manual (96.8%) and couples’ high rates of homework completion (82.0%). The intervention was acceptable to couples, based on high session attendance rates (97.4%) and treatment satisfaction ratings (7.39/10 for women, 7.33/10 for partners). The intervention produced moderate to large pre- to post-treatment improvements in women’s dyadic sexual desire for their partner (p = .002, d = 0.73) and couple members’ sexual distress (p = .001, d = -0.93 for women, p = .002, d = -0.54 for partners) that were maintained at 6-month follow-up. Couples also reported moderate improvements in sexual communication and satisfaction immediately post-treatment (ps = .001-.02, ds = 0.40-0.53), but there were little to no changes in relationship intimacy or satisfaction post-treatment (ps = .05-.84, ds = 0.10-0.19). Conclusions Findings show that a couple-based sex therapy intervention grounded in theory and dyadic research evidence reduces SIAD symptoms (greater sexual desire, lower distress) and more broadly improves couples’ sexual wellbeing (improved sexual communication, satisfaction; lower distress). The lack of change in relationship outcomes may have been the result of couples having relatively high relationship wellbeing as a prerequisite for participation in the study. Also, the focus of the CBCT intervention was on sexual, rather than relationship wellbeing. This pilot study was based on a small sample and had no control group by design. A randomized clinical trial of the CBCT intervention is needed. Disclosure No.