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Oilseed rape (<i>Brassica napus</i> L.) is a high-boron (B)-demanding crop, and initially, normal growing plants might show B deficiency at advanced growth stages on soils with marginal B availability. Hence, we compared the effects of B resupply via roots and leaves on growth and physiological response, and relative expression of B transporters in B-deficient oilseed rape plants. Four-week-old plants initially grown with inadequate B (1 µM B for the first two weeks and 0.25 µM B for the next two weeks) were later grown either as such with 0.25 µM B, with 25 µM B in nutrient solution or foliar sprayed with 7 mL of 30, 60 and 150 mM B solution plant⁻¹ as boric acid. Plants grown with 25 µM B in the nutrient solution from the beginning were included as adequate B treatment. Results showed that B resupply to B-deficient plants via roots and leaves (60 mM B) equally improved root and shoot dry matter, but not to the level of plants grown with adequate B supply. Foliar-applied 150 mM B proved toxic, causing leaf burn but not affecting dry matter. Resupply of B via roots increased B concentration in roots and leaves, while leaf-applied B did so only in leaves. Net carbon assimilation had a positive relationship with dry matter accumulation. Except for the highest foliar B level, B resupply via roots and leaves increased the accumulation of glucose, fructose and sucrose in leaves. Boron-deficient plants showed significant upregulation of <i>BnaNIP5;1</i> in leaves and roots and of <i>BnaBOR1;2</i> in roots. Boron resupply via roots reversed the B-deficiency-induced upregulation of <i>BnaNIP5;1</i> in roots, whereas the expression of <i>BnaBOR1;2</i> was reversed by both root and foliar B resupply. In leaves, B resupply by both methods reversed the expression of <i>BnaNIP5;1</i> to the level of B-adequate plants. It is concluded that B resupply to B-deficient plants via roots and leaves equally but partially corrected B deficiency in <i>B. napus</i> grown in hydroponics.