This experiment was carried out during two successive seasons 2015 and 2016 on the orchard of Faculty of Agriculture, Assiut University. This study aimed to investigate the effect of potassium sulfate (K) fertilizer at different rates, application times and method of application on yield parameters and fruit properties of old trees of Balady orange cv. The obtained results showed that all K treatments significantly increased the fruit set (%), number of fruits/tree, total yield/tree (kg), fruit weight (g), fruit height and diameter (cm) as compared with control (untreated trees) during both experimental seasons. Moreover, the three times applications and foliar sprays were more effective than twice applications and ground adding of potassium sulfate (K), respectively. The lowest values of these parameters, were recorded in control (untreated trees), while the foliar application of 666 g + 90 mlsprays /tree of potassium sulfate (K) three times gave the highest values during both tested seasons.