In the process of investigating the photosynthesis related genes, we obtained a recessive Arabidopsis thaliana mutant, yellow heart (yh). Compared with the wild type (Col0) A. thaliana, yh mutant appeared a yellow heart phenotype in new leaves. With mapbased cloning strategy, the mutant gene yh was precisely mapped into the 676 kb chromosome interval between the molecular markers INS1_55_342 and INS1_56_34 on chromosome 1. The yh mutant has a 4 base deletion at the splice junction of the 44th intron, which result in a change in the splice site of the intron. RTPCR results have indicated that the expression of yh gene is knock down, and yh mutant is indeed a new allelic mutation in gene At1g64790. Based on study above, yh mutant may provide a new genetic material to explore the chloroplast and leaf development mechanisms.