Abstract: The basic unit of muscle in chickens is myofiber, which is formed in the late embryonic stage. In order to understand the difference of myofiber characteristics during the late embryonic development among various chicken breeds, the differences in the histological development of myofibers of chicken breeds with different growth rates from four factors: breeds, embryonic ages,tissues and sexes were investigated. Qualified eggs of White Leghorn, Beijing-You Chicken, White Plymouth Rock and Cornish were selected for incubating to 15 embryonic age（ED15）, 17 embryonic age（ED17） and 1 day old（D1）. The pectoralis muscle and leg muscle were collected uniformly for paraffin section preparation and HE staining at the three points. The results showed that the sex had no significant effect on the histological characteristics of muscle fibers, while other three factors, namely embryonic age, tissue and breed, had significant effects on the histological characteristics of muscle fibers during the late embryonic period（P＜0.05）. The fusion of myoblast was essentially completed by ED17, after which the diameter of muscle fibers began to increase. The pectoralis muscle developed slowly during the late embryonic stage, and the leg muscle developed faster than the pectoralis muscle. The muscle fiber area of broiler chickens was significantly smaller than that of laying hens and Chinese chicken breeds（P＜0.05）, while the muscle fiber density was notably higher（P＜0.05）. The study suggested that ED17 was the cut-off point for myofiber formation in chicken embryos, and broiler chickens might have formed more muscle fibers during the embryonic stage.