This paper reports the use of an in vitro chemiluminescent method, ORAC_FL and SOD-like activity assays for the evaluation of antioxidant capacity of the whole buckwheat and its products after hydrothermal treatment. Phosphate buffer (0.75 mmol/L, pH 7.4) and 80% methanol (v/v) were used for the preparation of extracts originated from untreated buckwheat, hydrothermally-processed whole buckwheat, and obtained light groat and hull from the treated whole buckwheat. The antioxidative capacities of water- (ACW) and lipid-soluble (ACL) compounds were investigated by a facile chemiluminescence assay using a Photochem^® device. The superoxide dismutase-like activity (SOD-like activity) was evaluated as free radical scavenging activities of the extracts against superoxide anion radicals (O2¯^•) whereas Oxygen Radical Antioxidant Capacity (ORAC_FL) of the extracts was determined with the spectrofluorimetric assay. Moreover, the content of flavonoids in untreated buckwheat and its products after hydrothermal treatment was provided. The antioxidant capacity of the whole buckwheat before hydrothermal treatment evaluated with the chemiluminescence assay was formed mainly by lipid soluble antioxidants (ACL; 88.8 µmol Trolox/g d.m.) and only in part by the water soluble compounds (ACW; 5.1 µmol Trolox/g d.m.). The hydrothermal treatment of buckwheat whole grains caused a decrease in ACW and ACL by approximately 58% and 17%, respectively. The changes in the antioxidant capacity of untreated buckwheat and its products obtained after hydrothermal treatment were confirmed by the application of SOD and ORAC_FL methods. Antioxidant capacity of buckwheat material was related to changes in flavonoids composition provided by HPLC analysis.