The gray mould disease caused by Botrytis cinerea Pers., is one of the most postharvest economically important diseases of many plants all over the world. Potassium carbonate and potassium bicarbonate were tested to show their antifungal activities against the mycelia growth of the pathogen in vitro and in vivo on the postharvest gray mould on pepper fruits. Tested potassium salts, i.e. K2CO3 and KHCO3, reduced the growth of B. cinerea to 38.5 and 49.8%, respectively, after 7 days compared with the check treatment. In addition, among the tested materials for controlling pepper gray mould, carbonate and bicarbonate at concentrations of 1 and 2%, significantly reduced fruit rot severity, compared with Rovral WG 50% at 0.9g/l. Treating the undamaged pepper fruits with bicarbonate significantly reduced the gray mould infection. Also, submerging pepper fruits in the two tested salt solutions was more effective than spraying them. As for the best storage temperature, storing pepper fruits at 3°C followed by 13°C significantly decreased disease severity in all treatments. Also, changes in fruit weights as a result of infection under the influence of different storage temperatures were investigated. Treating pepper fruits with either carbonate or bicarbonate salt at 2%, led to enhance their resistance to gray mould disease and also decreased the loss in fruits weight and increased its shelf-life compared to check treatment.