To reveal the genetic variation, and loci involved, for a range of seed-related traits, a new F2 mapping population was developed by crossing Brassica rapa ssp. parachinensis L58 (CaiXin) with B. rapa ssp. trilocularis R-o-18 (spring oil seed), both rapid flowering and self-compatible. A linkage map was constructed using 97 AFLPs and 21 SSRs, covering a map distance of 757 cM with an average resolution of 6.4 cM, and 13 quantitative trait loci (QTL) were detected for nine traits. A strong seed colour QTL (LOD 26) co-localized with QTL for seed size (LOD 7), seed weight (LOD 4.6), seed oil content (LOD 6.6), number of siliques (LOD 3) and number of seeds per silique (LOD 3). There was only a significant positive correlation between seed colour and seed oil content in the yellow coloured classes. Seed coat colour and seed size were controlled by the maternal plant genotype. Plants with more siliques tended to have more, but smaller, seeds and higher seed oil content. Seed colour and seed oil content appeared to be controlled by two closely linked loci in repulsion phase. Thus, it may not always be advantageous to select for yellow-seededness when breeding for high seed oil content in Brassicas.