Background: Although conservative treatment has been used for unilateral retinoblastoma, enucleation is still the mainstay of treatment for the ICRB D–E group. In Japan, conservative treatment has been performed to preserve the eyes of patients with unilateral retinoblastoma including group D–E. We analyzed the data of patients treated at our institution with the aim of assessing if conservative therapy in the D–E group would worsen the survival outcomes and if it would also enable preservation of visual acuity. Procedure: We retrospectively reviewed medical records of patients of unilateral retinoblastoma from January 1, 2006, to December 31, 2015. Survival rates, EBRT-avoided preservation rates, and safety were analyzed for the initially enucleated and conservative treatment groups. Results: Among 153 patients, 34 (89%) in the B–C group and 49 (43%) in the D–E group underwent conservative treatment, respectively. 36 out of 83 (43%) patients were able to avoid enucleation without EBRT by undergoing conservative treatment. In the D–E groups with conservative treatment, there were extraocular recurrences in two patients, and one patient who had a CNS recurrence died. The 5-year OS and RFS was 97.9 (95%CI : 85.8–99.7)% and 95.8 (95%CI : 84.3–98.9)% in the D–E group, respectively. There were no acute serious adverse events during conservative treatment, and no secondary malignancies were observed. Conclusion: Conservative treatment for unilateral retinoblastoma, including for the D–E groups is acceptable based on the results that OS remained high and no serious adverse events were observed.