Background and Objective: Castanea crenata Sieb. et Zucc is a native species in Japan (Japanese chestnut). This species was reported to have very high antioxidant, allergic and anti-amnesic properties. The objective of the study was to evaluate the total polyphenols and antioxidant activities and analyse the bioactive compounds of this species. Materials and Methods: The flower of C. crenata was extracted by methanol and then the crude extract was fractioned by hexane, ethyl acetate, butanol and aqueous extracts. The extract and fractions were used to determine total polyphenols and antioxidant activities and to analyze bioactive components by gas chromatography-mass spectrometry (GC-MS). Results: The hexane fraction showed the highest amount of phenolic, flavonoid and tannin contents. This fraction also exhibited a higher reducing power at a concentration of 1 mg mL–1 than the other fractions and standard compound BHT (butylated hydroxytoluene). Methanol extract possessed the highest antioxidant capacity and significant stronger than BHT (pC. crenata flower. Methanol and ethyl acetate were found the highest number of compounds with 24 while butanol and water fractions included 20 compounds. The lowest number of constituents were identified in hexane with 7 compounds. Conclusion: Methanol and ethyl acetate were the most effective solvent to extract phytochemicals in the C. crenata flower, followed by butanol and water and hexane showed the least efficacy.