Agriculture is one of the most important sectors playing a significant role in non-oil exports in Iran. Among different agricultural products, pistachio is considered as an important horticultural crop consisting about 8% of the non-oil exports in Iran. Because of significant contribution in export income, applying appropriate approaches to increase the quality and yield of pistachio is necessary. In this one-year field experiment, effects of the foliar application of potassium (K) in the forms of mineral (K 2 SO 4 ) and complexed with lysine (K-Lys) and lysine plus methionine (K-Lys-Met) in the presence and absence of ascorbic acid (Asc) on yield and quality attributes of pistachio ( Pistachio vera L. cv. Owhadi) were evaluated. Lys and Asc alone treatments were used to distinguish the effects of accompanying Lys and Asc. A control treatment with no foliar application of amino acids and K was also used. Foliar spray treatments were applied on 22 June, 6 and 22 July, twice with 2 d intervals. Results showed that foliar application of K, regardless of the applied source, significantly increased leaf K concentration in comparison with control. Higher total yield, the fresh and dry mass of shelled and unshelled 100-nut, dry mass of kernels and percentage of non-split shells were obtained at the pistachio trees supplemented with K in comparison with those un-supplemented with K. Foliar application of K resulted in significant decrease of empties and abscission of inflorescence buds. The effectiveness of K-amino chelates in improving yield and quality attributes of pistachio was, in general, higher than K-sulfate. The highest yield and quality of pistachio was obtained with foliar application of K-Lys-Met (4:1). Higher efficiency of K-amino chelates in comparison with K-sulfate was associated with higher contribution of symplastic uptake of K in comparison with apoplastic retention. Accordingly, the accompanying amino acids, as natural traorters of cations, seems to be effective in higher translocation of K from the leaves to fruits. The critical deficiency concentration of K in the leaf and fruit to achieve the highest yield and quality of pistachio was 2.2 and 1.8%, respectively. The effect of fertilizer solution pH on K uptake by pistachio leaves wa also investigated. Based on the results, regardless of K fertilizer source (K-Lys and K-sulfate), K uptake by leaves decreased by increasing solution pH; although the magnitude of the decrease was higher for K-sulfate than that for K-Lys. The highest and lowest K uptake was obtained at pH 3.5 and pH 8, respectively. Keywords: Amino acid, Apoplastic retention, Fertilizer solution pH, Pistachio, Potassium, Symplastic uptake