The inhibitive effect of the natural juice of onion bulb on the corrosion of zinc in HCl solution was determined using hydrogen evolution and weight loss measurements as well as potentiostatic technique. Potentiodynamic anodic polarization was used to determine the effect of the juice on pitting corrosion of zinc in NaCl solution. It was found that the presence of onion juice reduces markedly the corrosion rate of zinc in the acid solution. The inhibition efficiency increases as the juice concentration is increased. Moreover, the presence of the juice in NaCl solution shifts the pitting potential toward more positive direction. The inhibitive effect of onion juice was discussed on the basis of adsorption of its components on the metal surface. Such adsorption is found to follows Langmuir adsorption isotherm. Negative values were calculated for the energy of adsorption indicating the spontaneity of the adsorption process. The formation of insoluble complexes as a result of interaction between the juice components and zinc cations was also discussed.