Sugar beet (Beta vulgaris L.) is one of the most important sugar crops worldwide. Despite the fact that sugar beet crop has high requirements for boron (B), the effect of B applications on seed yield and on seed quality is not known. A 2-year field study was conducted to determine whether soil and foliar B applications during anthesis increase seed set, final seed yield and improve seed quality of sugar beets. Boron solutions were applied at four rates (0, 245, 490 and 735 mg/l of B) as foliar applications and at two rates (1·5 and 3 kg/ha of B) as soil applications to field plots exhibiting no vegetative symptoms of B deficiency. Foliar B application increased the concentration of B in vegetative and reproductive tissues much more than soil application. In addition, foliar B application increased the seed yield by an average of 10% in the first year and by an average of 44% in the second year. The mean seed weight was affected by B application as it was increased in both years. The proportion of larger seeds (>5·00 and 4·5–5·00 mm) increased with increasing application of B. Moreover, seed quality was affected and the proportion of abnormal seedlings was decreased with B application. However, seed vigour was not affected by B application. These data indicate that foliar B application can improve seed yield and seed quality of sugar beet grown for seed production. However, the physiological basis of this effect remains unknown.