Plukenetia volubilis, whose seeds contain a high content of polyunsaturated fatty acids, produces approximately 60 male flowers but only 1–2 female flowers per inflorescence. Increasing the number of female flowers is critical for yield improvement of P. volubilis. In this study, we determined the effect of the plant growth regulator 6-benzyladenine (BA) on floral sex determination in P. volubilis. Exogenous application of BA converted male flowers on most of the inflorescences to female flowers, and approximately 8–20% of the induced female flowers further developed into fruits. Treatment with various concentrations of BA resulted in 3–41 female flowers per inflorescence, reaching the highest average of 23.9 at 160 mg/L BA treatment. There were 3–22 inflorescences with induced female flowers per branch on the trees treated with various concentrations of BA, and the highest average of 13.8 was observed at 20 mg/L of BA treatment. The average number of fruits per infructescence was 3.3 in the trees treated with the optimal concentration of BA (20 mg/L), compared with 1.3 for infructescences of the control trees. The results of this study show that BA is a plant growth regulator with the potential to induce floral feminization and promote fruiting of P. volubilis.