Phospho sulfonic acid (PSA) synthesized as an environmentally safe and efficient solid acid catalyst, and it used for the synthesis of several 2-disubstituted benzimidazoles, 2-substituted benzoxazoles, and 2-substituted quinoxalines in ethanol as a green solvent at ambient temperature is described. (i) A very simple, green and efﬁcient procedure for the synthesis of benzimidazole and also benzoxazole derivatives comprising the reaction of corresponding ortho-phenylenediamine or ortho-aminophenol with various aromatic aldehydes in absolute ethanol at ambient temperature is described. (ii) The direct condensation of various 1,2-diamines and carbonyl compounds in absolute ethanol at ambient temperature has been described to the synthesis of quinoxaline derivatives as biologically interesting compounds. Additionally, PSA is reused repeatedly for six reaction cycles without any evidence loss of activity. This green procedure offers significant advantages in terms of its simplicity, reusable strategy for the efﬁcient synthesis of benzimidazole derivatives, the elimination of corrosive liquid acids, short reaction time, high product yields, and simple preparation of the catalyst.