The synergistic inhibition effect of the 5-methyl-1H-benzotriazole (MBTAH)/1H-benzotriazole (BTAH) with potassium sorbate and gelatin on the copper corrosion in an acidic sulphate solution was investigated by electrochemical methods and weight loss measurements. According to the obtained results, potassium sorbate and gelatin act as mixed-type inhibitors. The inhibition efficiency was significantly greater in the presence of MBTAH/BTAH with potassium sorbate or gelatin which indicates that synergistic inhibition effect was achieved. Investigated compounds obey Langmuir adsorption isotherm. •The synergistic effect of 5-methyl-1H-benzotriazole and potassium sorbate was studied.•Also, the synergistic effect of 5-methyl-1H-benzotriazole and gelatin was studied.•Potentiodynamic polarization measurements, weight loss measurements and surface analysis were used.•The adsorption of the investigated inhibitors follows the Langmuir adsorption isotherm.