This study aimed to investigate the effects of testosterone replacement therapy (TRT) on lower urinary tract symptoms (LUTS) in men with late-onset hypogonadism (LOH) and to identify parameters predicting the efficacy of TRT in improving LUTS. This study included 60 consecutive Japanese men who were diagnosed with LOH and subsequently received TRT between January 2009 and December 2014. In this series, 250 mg of testosterone was injected intramuscularly every 3 or 4 weeks in all patients. The following parameters were retrospectively reviewed: body mass index (BMI), Aging Male Symptom (AMS) score, International Prostate Symptom Score (IPSS), International Index of Erectile Function–5 (IIEF-5) score, residual urine volume, prostate volume, serum levels of the prostate-specific antigen (PSA), and total- and free-testosterone levels before and 6 months after TRT. No significant differences were observed in BMI, residual urine volume, or prostate volume between surveys before and after TRT. The AMS score, IPSS, and IIEF-5 score were significantly improved and significant increases were noted in the serum levels of PSA and total- and free-testosterone levels after TRT. An analysis of IPSS subscores documented the significant improvement in storage symptom scores, but not in voiding symptom scores after TRT. Multivariate analyses of parameters assessed in this study identified the pretreatment AMS score, posttreatment IIEF-5 score, and prostate volume as independent predictors of improvements in IPSS following TRT. This study revealed that TRT appeared to have considerable therapeutic effects on LUTS, particularly on storage symptoms, in men with LOH.