Objective To observe the effect of continuous elastic outside distraction on the change of collagen content in female mini pig’s ni pples and their supporting tissues, and to investigate the mechanism of continuous elastic outside distraction correcting inverted ni pples. Methods Three 3-month-old female mini pigs (weighing 18.5-22.0 kg), which had 12 nipples, were employed. Four nipples of each minipig were not treated as control group (n=12), and the other nipples were continuously distracted with inverted nipple correction instruments as experimental group (n=24). The nipple specimens were harvested at 2, 4, 8, and 12 weeks after distraction and HE staining was performed to observe the change oftheir tissue structure. And saturated picric acid sirius red staining was used to observe the distribution and content of collagen types I and III, image analysis software for quantitative analysis. Results The control group had normal structure of epidermis at all time points. In experimental group, the epidermis thickened; basal cells, fibroblasts, and capillary significantly prol iferated along with the times; and the content and the density of collagen types I and III increased gradually. There were significant differences in collagen type I at 4, 8, and 12 weeks, and in collagen type III at 2, 4, 8, and 12 weeks between 2 groups (P lt; 0.01). There were significant differences in the ratio of collagen type I to III at 2 and 4 weeks between 2 groups (P lt; 0.05). Conclusion Continuous elastic outside distraction can increase the quantity of collagen types I and III in the tissue, the thickness of the dermis, and the height of the nipple, which may be one of key mechanisms of correction the inverted nipple by continuous elastic outside distraction.