Soybean is one of the most economically important crops in the world. The cotyledon is the nutrient storage area in seeds, and it is critical for seed quality and yield. Cotyledon mutants are important for the genetic dissection of embryo patterning and seed development.Here, we characterised a soybean curled-cotyledon (cco) mutant. Compared with wild-type (WT), the entire embryos of cco mutant resembled the “tail of swallow”. To explore the molecular mechanisms underlying soybean cotyledon development, we executed RNA-Seq using the Illumina HiSeq2000 system. Overall design: Pods at 7DAF collected from WT and cco were analyzed by RNA-seq.