BACKGROUND: The most common and debilitating side effects of radiation therapy (RT) for prostate cancer (PC) are fatigue, sleep disturbance, anxiety, and depression. Previous research has reported palliative benefits from certain self-management approaches, such as mindfulness meditation. OBJECTIVE: To develop, pre-test, and evaluate the feasibility, acceptability and initial benefit of brief, audio-based mindfulness delivered during daily RT for PC compared to a relaxing music control. METHODS: Following intervention development, participants were randomized to either brief guided mindfulness audio recordings or a relaxing music control during daily RT. A pre-testing phase was first conducted to determine optimal program start time, length, and content most associated with retention. A final program (n = 26) was delivered daily, starting on day one of week 2 of RT and lasting 4 consecutive weeks. Feasibility was defined as ≥70% on enrollment rate, retention, and audio program adherence. Acceptability was measured with a 12-item post-study survey. A secondary focus compared between group changes on patient reported outcomes of fatigue, anxiety, depression, sleep disturbance, and related outcomes at baseline and follow up assessments. Descriptive statistics and general linear models were used. RESULTS: Overall, 76% (n = 38) of approached men enrolled. Pre-testing retention rates were <70% while the final programs retention rate was 89%. The majority of acceptability criteria were met in both conditions, with relatively higher ratings in the mindfulness arm. Compared to music controls, mindfulness participants demonstrated significantly less uncertainty intolerance at 4-weeks (P = .046, d = .95); and significantly lower fatigue scores (P = .049, d = 1.3) and lower sleep disturbance scores (P = .035, d = 1.1) at the 3 months follow up. CONCLUSION: The final intervention met feasibility and acceptability criteria. Pre-testing refinements played a key role for optimal program delivery and retention. Audio-based mindfulness delivered during RT for PC hold potential to help decrease RT-related physical and emotional side effects.