Phthalanilic acid (PPA), a promising plant growth regulator, has been increasingly applied to fruit and vegetable production. However, its regulation on growth and development of cowpea (Vigna unguiculata) plants is still unclear. In this study, the physiological and biochemical effects of PPA on cowpea plants were investigated under field conditions by using brassinolide as the positive control. Here, the results showed that PPA treatments exhibited positive effects on photosynthesis. Meanwhile, antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) were enhanced post PPA application. In addition, free proline in cowpea leaves were increased, while the relative electrical conductivity and malondialdehyde (MDA) content were decreased. Furthermore, the length, width, single pod weight of cowpea were increased, and vitamin C, soluble protein and soluble sugar content were also improved by 200 mg·L-1 PPA. Moreover, PPA treatment increased yield by 16% when applied at 200 mg·L-1. Our findings demonstrate that PPA regulates the growth and development of cowpea plants, improving the yield and quality, especially at the concentration of 200 mg·L-1. This study indicates that PPA has an application prospect in cowpea production.