The pattern of walnut flowering varies depending on genetic and environmental factors. To study the patterns of walnut pistillate flowers developing as a result of applying gibberellic acid (GA 3 ), the research was conducted as a factorial design with 2 factors (three levels of trunk diameter (10 to 12 cm, 12 to 14 cm and 14 to 16 cm) and four levels of GA 3 (0, 50,100 and 200 mg/l)) on 'Chandler' commercial cultivar. Different levels of GA 3 were sprayed twice on the trees, i.e. 2 and 4 weeks after flowering. A new method was used to study the pistillate flower development based on hand-cut cross sections of bud and staining with methyl blue and carmine. Based on the results, different development stages included induction; initiation and differentiation of the pistillate flower bud were observed respectively in late May, early June, September and March. The results of GA 3 application showed that GA 3 treatment can alter the flowering pattern of walnut. GA 3 application significantly increased the number of male flowers, total flowers, and male: female flower ratio per branch. The number of female flowers increased by increasing the tree trunk diameter. The highest number of female flowers (62.3) was observed in trees with trunk diameters between 14-16 cm and application of 100 mg/l of GA 3 . Linear regression analysis showed a positive and strong relation between truck diameter with total flower number as well as female flower number.