Better fruit quality and higher yield are always the goals for horticultural crops. Extension of the effective pollination period (EPP) could improve fruit set and productivity by increasing pollen tube growth rate or prolonging ovule longevity. The present experiment was conducted for 2 years (2021 and 2022) in a commercial orchard in Khondab area of Markazi province, Iran, where the effect of phthalanilic acid (N-phenyl-phthalamic acid, PPA) on apricot (Prunus armeniaca L. cv. ‘Shekarpareh’) was investigated to extend the EPP and thus to increase the yield. PPA foliar spraying was carried out at the time of 80% flowering of the trees and concentrations of 0.0 as control, 400, and 800mg/L on 30 March. Also, half of the trees of each treatment were sprayed with complete liquid fertilizer with 4mg/L concentration on 30 May, and the other half were not fed. The results showed that the percentage of fruit set of trees treated with 400 and 800mg/L of PPA increased and had a significant difference compared with control trees, while non-significant differences were observed between trees treated with 400 and 800mg/L PPA in terms of that trait. In the trees treated with PPA that were not fed, the traits related to fruit size (length, width, and weight) showed a significant decrease compared with the control trees, while in the treated trees that were fed, there was a significant difference. There was no difference between control and treated trees in terms of fruit size. Based on the results of the present study, the use of 400–800mg/L PPA at the time of 80% flowering with nutrients is recommended to improve fruit set of ‘Shekarpareh’ apricot
