The increased industrial production of food, due to the rising world’s population, results with a large amount of agro-industrial wastes that represent environmental risk and economic losses. Therefore, nowadays, new ways of waste materials' valorization are investigated. Plant agro-industrial wastes consists mainly of outer layers of various fruits, vegetables and cereals, and are naturally rich, non-food innovative source of polyphenols. Onions and bananas are foods of extremely wide global consumption and their processing generates a significant amount of waste, the potential of which is not sufficiently exploited by the conventional methods of usage. The aim of this study was to characterize in detail the polyphenols in onion peel and banana peel by using polyphenol fractionation procedure, followed by the analysis of the isolated polyphenolic fractions using high performance liquid chromatography (HPLC-DAD). Quercetin and its glycosides have been identified as dominant compounds in onion peel: quercetin-4'-glucoside (7.40 mg gˉ¹), quercetin-3,4'-diglucoside (5.82 mg gˉ¹), quercetin (4.33 mg gˉ¹) and protocatechinic acid (1.03 mg gˉ¹), which are easily recovered by simple extraction using a combination of organic solvents and water. In banana peel, t-ferulic (2.02 mg gˉ¹) and p-coumaric acid (0.08 mg gˉ¹) were determined as dominant compounds, which can be recovered by alkaline hydrolysis since they are present in insoluble bound form. Onion peel and banana peel are valuable sources of polyphenols that can be recovered by appropriate procedures and used in creating functional food products.