Background/Objectives: Active surveillance (AS) is the recommended management strategy for localized, early-stage prostate cancer. Despite promising cancer-specific outcomes, up to one-third of men discontinue AS and undergo radical prostatectomy without evidence of disease progression, often because of stress, anxiety, uncertainty, and unmet supportive care needs. Evidence-based psychosocial interventions tailored to men on AS are lacking. We aimed to: (1) adapt the Stress Management and Resilience Training (SMART) program to address the unique psychosocial and supportive care needs of men with prostate cancer on AS (SMART-AS), and (2) evaluate the feasibility and acceptability of SMART-AS. Methods: Following the Assessment, Decision, Adaptation, Production, Topical Experts, Integration, Training, Testing (ADAPT-ITT) framework, we adapted SMART for men with prostate cancer on AS (SMART-AS) informed by our prior qualitative study and expert input. Next, we conducted a single-arm pilot feasibility study at one large urban academic medical center. Participants attended eight weekly 90-minute telehealth group SMART-AS sessions. Feasibility and acceptability were evaluated one-week post-intervention. Results: Based on our prior qualitative study and expert input, core SMART-AS components included content targeting stress, anxiety, communication, and self-management. In total, 30 participants were enrolled in the pilot feasibility study and completed baseline assessments (mean age = 71 years, standard deviation = 8.3); 26/30 (86.7%) completed six out of eight SMART-AS sessions, and 17/30 (56.7%) completed post-intervention assessments. Nearly all (16/17, 94.1%) reported that they would recommend SMART-AS to others. Most agreed that SMART-AS helped them talk to clinicians (13/17, 76.5%), reduced anxiety (13/17, 76.5%), enhanced coping skills for AS challenges (15/17, 88.2%), and supported self-care (15/17, 88.2%). Nearly two-thirds (11/17, 64.7%) reported SMART-AS helped them continue AS as a management strategy. Conclusions: This pilot study provides preliminary evidence supporting the feasibility and acceptability of SMART-AS among men with prostate cancer on AS. Participants reported perceived improvements in anxiety, coping, communication with clinicians, and self-management. Findings support further evaluation in a randomized controlled trial.