Objective To investigate the periodical changes of hair follicles and establish animal models for studying the follicle developmental process.Method The morphology of skin hair follicles of Kunming strain mice was observed by histology during early development stage(from embryonic day 16 to postnatal day 19).Result The embryonic mouse skin epidermis had deep wrinkle,the number of wrinkles decreased on postnatal day 3 to day 5,and the wrinkles became shallow.Depth of epidermis and dermis increased stably during E16 to E19,but it reduced sharply after birth.The epidermis increased slowly stably from postnatal day 1 to day 9,the dermis increased sharply after birth.Primary hair follicles could be seen in E16 skin,the hair follicle density increased.In contrast to primary ones,secondary hair follicles appeared in E18 skin,secondary hair follicle density increased sharply and up to 1257.14/mm after postnatal day 7.The length and depth of the primary and secondary hair follicles changed a little near birth,but changed obviously from postnatal day 3 to day 7.Conclusion The changes of the mouse skin structure,primary and secondary hair follicles and the depth and length of the hair follicles are present not only in embryos but also in the early postnatal period, and in this time there is still rapid development.Mouse skin begins to change periodically.It is best to study the hair follicle gene expression in the period from E16 to postnatal day 7.