Background: We assessed the outcomes of the patients with pT0 on first protocol biopsy during active surveillance(AS) from the analysis Japanese cohort forming part of the Prostate Cancer Research International: Active Surveillance (PRIAS) study. Methods: PRIAS-JAPAN started in January 2010. 39 institutions are participating in this study. The inclusion criteria for the PRIAS study are as follows: clinical stage T1c/T2, PSA ≤ 10 ng/ml, PSA density (PSAD) < 0.2 ng/ml per milliliter, one or two positive biopsy cores, and Gleason score (GS) ≤ 6 at initial diagnostic biopsy.In this analysis, we defined the patients presenting no reclassification with cancer after first protocol biopsy as NR-CA group and the patients presenting no reclassification showing pT0 as NR-noCA group. We compared AS remaining rate, pathological outcomes in extra biopsy and second protocol biopsy at 4 years between two groups. Results: First protocol biopsy was performed on 514 patients. 191 patients were in NR-noCA group and 199 patients were in NR-CA group. Patients background of NR-noCA group was as follows: Median age was 68, median PSA was 5.6ng/ml, and median prostate volume was 38.4cc. T1c were in 183 and T2a were in 8. At the time of first protocol biopsy, there was no significant differences about PSA parameters and pathological factors between NR-noCA group and NR-CA group. Also, extra biopsy performing rate (NR-noCA group vs NR-CA group; 5.75% vs 7.53%) and implementation rate of second protocol biopsy at 4 years (75.6% vs 63.6%) showed no significant differences. On second protocol biopsy, number of cancer positive cores were significantly smaller and rate of pT0 was higher in NR-noCA group. After five years, both group showed comparable AS remaining rate (76.9 vs 75.3%). Thirty eight patients of NR-noCA group selected definitive therapy and surgery was the most frequently chosen treatment option. Conclusions: Although rate of pT0 on second biopsy was higher in NR-noCA group, there was no significant difference between both groups in AS remaining rate. The patients in NR-noCA group tended to choose surgery as a definitive therapy. Clinical trial information: UMIN000002874.