Abstract: Analytical results are reported in this paper on peroxidase isozyme in 86 accessions of the four species of Lycopersicon——L. peruvianum Mill., L. hirsutum Hurnb. ct Bonp, L. pimpinellifolium (Jusl) Mill. and L. esculentum Mill. in the 15 different stages of development and in several organs of the plant by means of continuous concentration gradient polyacrylamide gel (7.5-15%) electrophoresis. The results indicate that overlap-pile up peroxidase isozyme patterns show 28 bands in L. peruvianum, 29 bands in L. hirsutum, 28 bands in L. pimpinellifolium and 27 bands in L. esculentum, and that peroxidase isozyme patterns show remarkble difference among the four species and no difference in each one; and that changes of zymogram patterns and activities of peroxidase with different stages and with different organs of the plant are similar in the roots, the stalks and the leaves but different in the fruits among the four species.Some problems concerning the significance of the value of similarity of the isozyme patterns and applications of the wild species and isozyme analysis in tomato breeding are also discussed in the last part of the paper.