Due to the increasing demand for biofuel production, it is an important goal to optimize the seed productivity and quality of oilseed plants even in adverse conditions. Acting on signalling mechanisms might provide means to attain such goals. In this study, we were interested in the effect of a brassinosteroid hormone 24-epibrassinolide (24-EBR) on Brassica napus cultivated in salt stress condition. We show that salt stress leads to a 60 % decrease in seed production in B. napus. This is accompanied by a 50 % decrease in seed oil content. Treatment with 24-EBR had no effect on seed and oil productivity in control plants. However, it could rescue half of the seed production and all the oil production in salt-treated plants. The fatty acid composition of seed oil in B. napus was selectively affected by salt stress, 24-EBR or combined treatment. Besides these long-term actions of 24-EBR, we have also investigated its short-term actions in cell signalling. We did so by in vivo labelling of plantlets with fluorescently labelled phosphatidylcholine. A treatment of 2 h with 24-EBR was sufficient to induce a substantial increase in the content of diacylglycerol and phosphatidic acid, two lipid mediators. Non-specific phospholipases C and phospholipases D are involved in these increases. Therefore, brassinosteroid treatments appear as promising way to gain oil productivity when plants have to grow in unfavourable conditions such as salt stress. The link between long-term actions and short-term signalling of 24-EBR is discussed.