In order to evaluate the effects of foliar application of potassium sulfate on some quantitative and qualitative characteristics of three olive (Olea europaea L.) cultivars, two split plot field experiments, arranged in complete block designs with three replications, were carried out through 2012–2013 in an orchard located in Ahvaz, Khuzestan province, Iran. Three olive cultivars (Mission, Coronaiki and Dezfuli) and three foliar applications of potassium sulfate (0, 1 and 2 g.L-1) were randomized in main plots and sub-plots respectively. The interaction effect between year and cultivar was significant for fruit fresh weight, dry weight of fruit pulp, stone weight , pulp: stone ratio, oil content (P≤0.01) and fresh weight of pulp (P≤0.05). Also, the interaction effect between year and foliar potassium application was significant for fruit fresh weight, dry and fresh weight of fruit pulp (P≤0.01) and stone weight (P≤0.05). The interaction between cultivar and foliar application of potassium sulfate for fruit fresh weight, dry and fresh weight of fruit pulp was significant at 1% probability level. In addition, interaction effect between year, cultivar and foliar application of potassium sulfate was significant for fruit fresh weight, dry and fresh weight of fruit pulp, oil content of the fruit pulp (% D.W.) at 1% probability level, and other traits at 5% probability level. Thus, it can be concluded that annual variability in the growth environment had an important effect on the parameters studied in this experiment. Dezfuli cultivar had more oil content than other cultivars that could be due to genetic diversity among cultivars for using sources in enhancement oil content and also more compatibility with the environmental conditions in this area. Foliar application of potassium sulfate increased unsaturated fatty acids and decreased saturated fatty acids in Dezfuli and Coronaiki cultivars. The highest content of oleic acid and oleic acid: linoleic acid ratio (60.54 % and 8.38) was found in Coronaiki cultivar with foliar potassium application (2 g.L-1) and the lowest amount in Dezfuli cultivar with control treatment (48.90 % and 1.67). Therefore, year conditions as well as foliar application of potassium sulfate can have a positive impact on ftuit weight, percentage of olive oil and fatty acid composition.