Pot experiments were conducted to study the effects of boron on floral organs development and seed-setting of rapeseed (Brassica napus L.).The results are as follows: In boron-free (B₀) and boron-normal (B₁) plants, boron concentrations of floral organs were greater than those of leaves, especially with boron in pistil and stamen twice as high as that in leaves. But leaves had the greatest boron concentration when boron was excess (B₂). Boron deficiency led in reduction of the length and weight of stamen and in abnormality of anther tapetum development. Differentiation of pollen sac was inhibited. It was found that both boron deficiency and excess reduced the numbers of effective siliques per plant and seeds per silique, rate of siliques, rate of seed-setting, and rape seed yield. The effect of boron on the number of ovules per silique was not significant. Compared with Ningyou No.7 (a high erucic acid type), Ningyou No. 8 (a low erucic acid type) was more sensitive to boron-deficiency and boron-excess.