Carotenoids and sinapate esters in Brassica napus affect the nutritional value of the seed. In this study, the B. napus regulatory gene DE-ETIOLATED1 (DET1), which is a negative regulator of light-mediated responses in plants and affects carotenoid and flavonoid pathways in tomato, was suppressed both constitutively and in a seed-specific manner by RNAi. Constitutive silencing of DET1 resulted in transgenic seeds with substantially elevated levels of lutein, β-carotene, and zeaxanthin relative to nontransgenic seeds. Levels of these carotenoids were also enhanced but to a lesser extent in seeds of transgenic plants with seed-specific silencing of DET1. Moreover, sinapate esters 1,2-disinapoylgentiobiose and 1,2-di-O-sinapoylglucose were identified in the seeds using 1D and 2D NMR, as well as ESI-MS spectrum analyses. The levels of 1,2-di-O-sinapoylglucose in seeds in both sets of transgenic plants were lower compared to nontransgenic seeds. The results revealed that DET1 suppression in B. napus can increase the levels of carotenoids and reduce the levels of sinapate esters simultaneously in the seeds, thus enhancing their overall nutritional value.