The mutant R24-12-6 with a leaf yellow which induced by 60Co - γ radiation from pepper wild type 6421was used as the material to compare the differences of agronomic characters, chloroplast ultrastructure, physiological and biochemical characteristics between the mutant and the wild type pepper 6421. The results showed that mutant R24-12-6 was inherited by recessive single gene. The fruit length of mutant R24-12-6 was 2.06 cm higher than that of the wild type 6421. The fruit width, fruit number and single fruit quality of mutant R24-12-6 were lower than those of the wild type, among then fruit number showed significant difference. The contents of chlorophyll, chlorophyll a, chlorophyll b and carotenoid decreased significantly compared with wild type 6421. The net photosynthetic rate, transpiration rate, stomatal conductance and inter-cellular CO2 concentration of mutant R24-12-6 were lower than those of the wild type, which accounted 84.80%, 87.96%, 98.16% and 80.51% of those of the wild type of 6421, respectively, but with no significant differences.Transmission electron microscopy showed that the number of chloroplasts decreased and the lamellar structure of basal grains decreased in leaf yellow mutant.