Medicago truncatula, soybean (Glycine max), Arabidopsis thaliana and rice (Oryza sativa) all belong to the core angiosperm group of plants. Seed-specific genes are important for seed formation and development in these angiosperms. The identification of genes specifically expressed in angiosperm seeds and the comparison of the expression patterns of homologous genes among different angiosperm species can provide novel insights into the functions of genes that control seed development and the evolution of angiosperms. We downloaded the sequences and expression data from the relevant databases, and the seed-specific expression of genes was identified with cut-offs of a gene expression level ratio ≥ 5 and a Z-score ≥ 6. The genes were analysed using local BLAST software with an E-value ≤ 1.0E − 505. A total of 605, 581, 778 and 722 genes showed specific expression in the seeds of Medicago, soybean, Arabidopsis and rice, respectively. Additionally, we compared the expression patterns of seed-specific genes from each species with their homologues in the other three species, and found that the degree of variation in the expression patterns of homologous genes was low among closely related species but higher among more distantly related ones. The discrepancy between the homologous gene expression patterns may be caused by the different characteristics of the cis-elements in the promoter regions of the homologous genes.