Background: The purpose of this trial was to prospectively evaluate the short-term outcomes of moderately hypofractionated intensity-modulated radiation therapy (MH-IMRT) for localized prostate cancer. Methods: In November 2013, we started a pilot study of MH-IMRT for prostate cancer. Eligible patients were 50 to 80 years old and had D’Amico’s low- or intermediate-risk disease. Fifty-four Gy in 15 fractions (3.6 Gy per fraction), in which the equivalent total dose in 2-Gy fractions to prostate cancer was estimated about 78 Gy, were delivered over 3 weeks using image-guided IMRT based on daily cone beam CT without intraprostatic fiducial markers. Neoadjuvant androgen deprivation therapy was given 4 to 8 months before the start of IMRT. The primary endpoint was incidence rates of acute toxicities, and the secondary endpoints were incidence rates of late toxicities at 2 years and biochemical relapse free survival (BRFS) at 2 years. Acute toxicities were evaluated based on the Common Terminology Criteria for Adverse Events version 4.0 criteria. Late toxicities were evaluated based on RTOG/EORTC Late Radiation Morbidity Scoring Schema. Biochemical relapse was defined according to the Phoenix definition (absolute nadir + 2 ng/ml). The planned sample size was 25 patients. Results: Twenty-five patients were enrolled in this trial. Twenty-four patients were treated with MH-IMRT, and 1 patient was treated with conventionally fractionated IMRT because his small intestine was close to the target. The median age in the cohort was 71 years old, and median follow-up period was 31 months (range 24-42). Four patients (17%) had low- and 20 (83%) had intermediate-risk disease. No grade ≥3 acute toxicity was observed and the incidence rates of grade 2 acute genitourinary and gastrointestinal toxicities were 21% and 4%, respectively. So far no grade ≥2 late toxicity has been observed and the 2-year BRFS is 95.8%. Transient PSA elevation over 0.4 ng/ml was observed in 11 patients (46%) and in 5 patients (21%) PSA rose ≥1.0 ng/ml above nadir. Conclusions: Sort-term outcome of MH-IMRT delivering 54 Gy in 15 fractions over 3 weeks for prostate cancer was comparable to that of conventionally fractionated IMRT. Clinical trial information: UMIN000012057.