Consumer demand for bakery products prepared using composite flour, such as biscuits, is growing. The incorporation of buckwheat flour, soy flour, and kinema flour can be considered in composite flour-based biscuits since they have good nutraceutical properties and their gluten-free nature can help avoid celiac disease. The purpose of this research was to study the physicochemical and functional characteristics of buckwheat flour, soy flour, and kinema flour as well as their potential as functional foods. The biscuits were prepared with a mixture of buckwheat flour, kinema flour, and soy flour in 10%, 30%, and 50% concentrations with whole wheat flour to evaluate the quality and acceptability of the biscuit. The composite flour biscuits were examined for their proximate compositions. The DPPH radical scavenging assay was used to assess the antioxidant properties of the biscuit extract, while the Folin-Ciocalteu method and the Aluminum Chloride Colorimetric Assay were both used to assess the total phenolic and flavonoid contents, respectively. The overall acceptability of biscuits by sensory analysis was highest at a 50% level of Black kinema flour (BLKF). Sample M (BLKF 50 %) had 0.66, 21.06, 1.61, 11.88, and 3.23 % moisture, fat, crude fiber, protein, and ash, respectively. The highest total phenolic and total flavonoid contents were found in black kinema flour (748.22 mg GAE/g and 8.92 mg GAE/g, respectively), while the highest level of antioxidant activity was found in brown kinema flour (313.56 μg/ml). BRKF 50:50 had the highest antioxidant activity (440.43 μg/ml), while BLKF 50:50 had the highest total phenolic and flavonoid contents (692.67 mg GAE/g and 8.60 mg GAE/g, respectively). The qualitative evaluation of the phytochemical content and amino acid in various flour varieties as well as in composite biscuits gave positive results. Thus, the composite flour biscuits could serve as a low-cost functional food.