Several sea-slug species sequester chloroplasts in cells of the digestive diverticula from its food algae. The sequestered chloroplast keeps the photosynthetic activity in the sea-slug cell for several months and provides saccharides and amino-acids for the sea-slug. Because the food algal chloroplast DNA lacks several genes for photosynthesis, it is mysterious how the kleptoplast keeps the photosynthetic reactions for over several months in the sea-slug cell. Some genomic studies are in progress about the sea-slug. However, the keeping mechanism of the photosynthetic activity is still unclear. In this study, we tried to gain the transcriptome data of a donor algal species of kleptoplasts, Halimeda borneensis, to find the horizontally transferred algal genes from the sea-slug genomic data.