Sunflower is considered highly demanding in boron (B); however, it has low efficiency in using this micronutrient. An experiment under protected cultivation was carried out to evaluate the effects of boron fertilization on nutrition and sunflower biomass production (Helianthus annuus). A completely randomized design with four replications was used. Five boron doses: 0 (Control), 1, 2, 3, and 4 kg ha-1, were applied to the soil using boric acid as the source. Biometric assessments, measurements of the relative chlorophyll index (RCI), production of dry biomass and the boron use efficiency by plants were carried out. The data were subjected to analysis of variance and F test (p<0.05), with polynomial regression analysis when significant. Leaf area, RCI evaluated at 15 and 60 days, and biomass increase linearly according to the boron application up to the dose of 4 kg ha-1, which corresponds to an increase of 31, 12, 14, and 61%, respectively, compared to control treatment. However, for plant height and nutritional efficiency, the best results were obtained with the dose of 2.64 kg ha-1 of B, with a decrease in higher doses. Boron fertilization in sunflower crop positively influences the nutritional and growth aspects of plants. In general, the application of up to 3 kg ha-1 of B in soils with low natural content increases the crop yield, without phytotoxicity aspects caused by the nutrient