Cranberry powder (CR) is reported to be effective against lower urinary tract symptoms (LUTS) and recurrent urinary tract infections. Benign prostatic hyperplasia (BPH) in men older than 50 years is a common cause of LUTS. Here, we attempted to evaluate if CR is also effective for treating BPH using a BPH-induced rat model, which was orally administered CR. Male Sprague-Dawley rats weighing 200–250 g were randomly divided into the following six groups (n = 9): noncastration group; castration group; BPH group; BPH and cranberry for 8-week (CR8W) group; BPH and cranberry for 4-week (CR4W) group; and BPH and saw palmetto group (saw palmetto). Compared with the BPH group, the CR8W group showed a significant decrease in prostate weight (by 33%), dihydrotestosterone (DHT) levels (by 18% in serum and 28% in prostate), 5-alpha reductase levels (18% reduction of type 1 and 35% of type 2), and histological changes. These results indicate that CR could attenuate BPH by inhibiting 5-alpha reductase and by reducing other biomarkers such as prostate weight and DHT levels. Thus, CR may be an effective candidate for the development of a functional food for BPH treatment. IACUC (USW-IACUC-R-2015-004).