Thefood preservatives potassium sorbate or sodium carbonate were evaluated to study their effect on green and blue moulds incidence of navel orange fruits. Potassium sorbate and sodium carbonate at concentration of 4.0% completely inhibited the linear growth and spore germination of Penicillium digitatum and P. italicum. Fresh navel orange fruits were artificially wounded and inoculated with spore suspension (10⁶ spores/ml) of P. digitatum or P. italicum then dipped in potassium sorbate or sodium carbonate at different concentrations then air dried and stored for 15 days. The most effective treatment was potassium sorbate at concentration of 4.0% which reduced the disease incidence and rotted part tissue by 80.0 & 89.0 and 83.3 & 90.0% for blue and green moulds, respectively. Diameter of inhibition growth zone of both fungi gradually increased as salt concentrations increased, individually or combined with water wax. In other experiment, potassium sorbate and sodium carbonate were mixed with carnova wax to study their durable protective effect against green and blue moulds incidence on navel orange fruits during 45 days of storage. All treatments have significantly reduced both diseases incidence and rotted part tissue during 45 days. The highest reduction was obtained with potassium sorbate at concentration 4.0% which reduced the blue & green moulds incidence and rotted part tissue more than 90.0 and 92.0%, respectively. While, potassium sorbate al concentrations of 2.0% and sodium carbonate at 4.0% reduced both diseases incidence and rotted part tissue more than 80.0 and 84.0%, respectively. So, postharvest application of potassium sorbate or sodium carbonate could be considered for controlling postharvest diseases of navel orange fruits.