Cyanobacteria are unique prokaryotes performing plant-like photosynthesis and important organisms with valuable genes. We cloned Slr1515 from the cyanobacterium Synechocystis sp. PCC 6803. The Slr1515 was introduced into rice (Oryza sativa L. subsp. japonica cv. ‘Zhonghua 11’) by Agrobacterium-mediated transformation and verified by PCR and immunoblot analysis. Transgenic rice seeds were selected by GFP reporter signals, then seedlings underwent phenotype analysis. Agronomic traits such as chlorophyll content and flag leaf length were better in transgenic plants carrying Slr1515 than non-transgenic plants. These observations provide preliminary information for improvement of rice performance.