Four isolates of Phomopsis psidii were obtained from naturally rotted fruits of guava, cvs. Maamora and Balady. They were proved to be pathogenic to guava fruits at and at room temperature. Disease incidence (DI%) and disease incidence (DS%) were greatly reduce at 8±1°C compared with 100% Dl and 83% DS were recorded at room temperature, 15 days after inoculation. Fruits pre-treated with salicylic or citric acids showed highest decrease in DI and DS% of rot when fruits were stored at room temperature, whereas no infection was recorded in SA-treated fruits after 15 days of cold storage. When fruits were stored on 8±1°C, then treated with CaCl₂ or SA and stored at room temperature, no symptoms were detected till 6 days, shelf-life period.  Pre-treated fruits with CaCl₂ and SA, also, exhibited the lowest loss of weight values, either in inoculated or non-inoculated fruits. Total soluble solids content increased gradually, in all treatments, till the end of experiment in non-infected fruits, but in case of infected ones, the TSS% decreased after 10 days of stored period, except in fruits treated with CA which exhibited 9% increase until the end of storage period. Ascorbic acid (AA) % decreased gradually weight advanced storage. The percent of reduction in AA was higher in infected fruits than in non-infected ones. Fruits pre-treated with CaCl₂, SA or CA contained AA more than control. The highest values of total sugar content (8.8 - 8.3 %) were recorded in fruits treated with SA, CA and H₂O₂, respectively, while the least values (7.4%) was recorded in fruits treated with CaCl₂ (27.1% increase than control).