Retinoblastoma is reported as a rare cancer that occurs during childhood. Although several treatments are available for retinoblastoma, there is a need for alternative new treatment modalities for retinoblastoma with better safety and efficacy profile. Galangin (3,5,7-trihydroxyflavone), is a flavonoid compound, which is found in high concentration in lesser galangal. Galangin has been reported to have various bioactivities, including anti-inflammation, anti-oxidative stress and anti-cancer through various pathways. The objective of our study was to explore the effects of galangin on the suppression of retinoblastoma in vitro and in vivo. Using MTT analysis, transwell-chamber migration analysis, colony-forming analysis, wound healing analysis, immunofluorescent assay of KI-67, we found that galangin exhibited a suppressive effect on human retinoblastoma cell proliferation and migration. Moreover, PTEN, a tumor-suppressor, was increased by galangin in cancer cells and in tumor tissues isolated from retinoblastoma xenograft models. Additionally, galangin reduced protein kinase B (Akt) phosphorylation, which was associated with PTEN up-regulation. Galangin-reduced Akt activation and cell proliferation was abolished by PTEN knockdown, which might be associated with the over-expression of phosphatidylinositol-3,4,5-triphosphate (PIP3)/diphosphate product (PIP2). Furthermore, flow cytometry, Hoechst 33258 staining and western blot assays indicated that galangin could induce apoptosis through promoting Caspase-3 pathway, which was, at least partly, dependent on PTEN expression. Our data illustrated that galangin treatment suppressed the growth of retinoblastoma tumor in vivo by anti-proliferative and apoptogenic mechanisms. Thus, galangin might be a safe and promising non-chemotherapeutic drug, which could be useful as an adjuvant against retinoblastoma.