The application of biostimulants in agriculture has been used to increase crop yield. This study evaluated the effects of exogenous application of thiamine and nicotinamide on soybean plants. The experiment was conducted in Cassilândia, MS. The randomized blocks design with 5 treatments and 8 replications was used. The treatments consisted of concentrations of nicotinamide and thiamine at 0, 50, and 100 mg L-1 of water, applied exogenously when the plants were at the V3 stage. Gas exchange, number of grains per pod, number of pods, and grain yield were assessed. Plant height was increased by applying vitamins, with all treatments outperforming the control. The application of nicotinamide or thiamine at doses between 50 and 100 mg L-1 favors the development and grain yield of soybean plants, making it possible to use them as a biostimulant.