Plant yellow-green leaf mutant plays an important role in a series of basic studies such as photosynthesis, synthetic metabolic pathway of chlorophyll, genetic differentiation and development of chloroplast, as well as a marker trait to breeding research. In this study, we analyzed the phenotypic characteristics and photosynthesis of a tomato yellow-green leaf mutant that was generated by chemical mutagenesis. We found that the yellow-green phenotype of mutant (mu) became visible in the first true leaf. The mu plant showed dwarfism, the reduction of chlorophyll content and net photosynthetic rate in relative to that of the wild type M82. By analyzing the ultra-structure of chloroplast with transmission microscope, the chloroplast thylakoid was impaired development in the mu mutant. By genetic analysis between mu and M82, the segregation ratio (3:1) was observed in the seedlings with normal and yellow leaves in a F2 population, supporting a single recessive gene underlying the mutated yellow-green phenotype. Thus, this study identified a chloroplast-abnormal mutant that might be useful in exploring the signaling in nucleus and chloroplast, for example, by isolating the target gene controlling the yellow-green phenotype of leaves.