Abstract: The evaluation of the effect of phthalanilic acid on the endogenous hormone, fruit quality and yield is of great importance for its rational use in crop production. In this study, the effects of phthalanilic acid (133.3, 200.0 and 266.7 mg/L) on the endogenous hormone content of leaves, fruit quality and yield of pepper (Capsicum annuum L.) plants was investigated in field plot experiment by physiological and biochemical methods such as enzyme-linked immunosorbent assay, with brassinolide as the control agent. Compared with the blank, phthalanilic acid treatments could increase the content of auxin (IAA) in pepper leaves by 4.15%-28.54% and the content of zeatin (ZT) by 23.41%-163.10%, while decrease the content of abscisic acid (ABA) by 5.47%-28.97%, and it had no obvious effect on the content of gibberellin (GA₃), at the bud, flowering and fruit stage. after treated by phthalanilic acid, the IAA/ZT ratio in pepper leaves was decreased first and then increased, while the ratio of IAA/ABA, ZT/ABA, GA₃/ABA were increased during the three stages. The content and ratio of endogenous hormone in pepper leaves were also significantly affected by the brassinolide treatment, but the influence was different from that of the phthalanilic acid treatments. Compared with the blank, phthalanilic acid treatments could significantly improve the fruit quality of peppers. The single fruit mass, fruit shape index and dry weight (per 100 g fresh fruit) was improved by up to 14.75%, 49.67% and 26.09%, respectively. And the contents of soluble sugar, soluble protein, vitamin C and capsaicine were increased by 69.75%-99.62%, 29.17%-94.32%, 15.86%-55.35% and 1.82%-31.69%, respectively. The total yield was increased by 20.66%-37.19% after the phthalanilic acid treatment compared with the blank. Brassinolide treatment could also enhance the fruit quality and the yield of peppers. Especially, the yield was significantly increased by 38.02% compared with the blank. However, the overall improvement of fruit quality was less satisfied compared to phthalanilic acid. Overall, phthalanilic acid has positive impact on the content and ratio of endogenous hormone in peppers, and it can also improve the yield and quality of peppers. However, its mechanism and influence on peppers are different from those of brassinolide. The recommended dosage of phthalanilic acid is 133.3-200.0 mg/L for pepper plants in the field.