Abstract: Starch is produced by most green plants as an energy store and is also a major carbohydrate source in human diet. There are two stages of starch synthesis in most plants. In the first stage, transient starch is produced during photosynthesis, and in the second, the nutrition accumulation stage, starch is deposited for storage purposes. Although the first stage of starch synthesis plays a critical role in carbohydrate metabolism, starch biosynthesis in photosynthetic organs has received less attention. To detect the evolutionary patterns associated with starch synthase, the enzyme involved in the biosynthesis of starch, in plant photosynthetic organs, we used leaf transcriptome resequencing to investigate the genotype and expression divergence of the gene family in Oryza officinalis. Eight complete starch synthase genes were identified, and phylogenetic analyses confirmed that the genes were SSI, SSII, SIII, SSIV, SSV, and GSBBII. Comparison of sequences and expression quantities showed that the evolutionary patterns of the starch synthase family in O. officinalis were highly consistent with those of cultivated rice. The homologous sequence identities between the two species were 95% to 98% at the mRNA level. Further statistical tests based on the ratio of nonsynonymous to synonymous substitutions indicated that all eight genes were under significant purifying selection. In addition, three genes specifically expressed in the endosperm of cultivated rice were not found in the leaf transcriptome of O. officinalis. However, four genes with predominant expression in the leaves of cultivated rice showed relatively higher expression in the O. officinalis leaf transcriptome.