Abstract: LI Xue*, ZHOU Mei-hua, WU Di, SUN Jie, ZHU Wen-yuan, ZHAO Wen-e, LU Yan. *Department of Dermatology, First Affiliated Hospital of Nanjing Medical University, Nanjing 210029, China Corresponding authors: ZHAO Wen-e, Email: zwe99@126.com; LU Yan, Email: luyan6289@163.com 【Abstract】 Objective To evaluate the changes to mitochondrial ultrastructure in melanocytes of perilesional skin from patients with vitiligo. Methods Skin specimens were obtained from the perilesional area （0.5 － 1 cm distal to vitiligo lesions） of 10 patients with progressive vitiligo and 10 patients with stable vitiligo, as well as from the normal skin of 10 healthy volunteers. The morphology of melanocytes was observed by using transmission electron microscopy （TEM）. Besides, stereological parameters of mitochondria, such as volume density （Vv）, surface density （Sv） and numerical density （Nv）, were measured. Results In melanocytes from the healthy controls, there were a large number of melanosomes with the number of melanosomes per melanocyte being 28.57± 3.21, which were mainly at stage Ⅲ and Ⅳ; mitochondria with normal structure and densely packed cristae were regularly arranged; autophagosomes were seen occasionally. Compared with the melanocytes from healthy controls, there was an obvious decrease in the number of melanosomes （especially stage Ⅲ melanosomes） in melanocytes from the perilesional skin of patients, with the number of melanosomes per melanocyte being 22.00 ± 6.16 （P < 0.05） and 17.43 ± 6.24 （P < 0.05） in patients with progressive vitiligo and stable vitiligo, respectively. TEM also showed disorganized or disrupted mitochondria in various shapes and sizes, most of which were swelling with obscure cristae and vacuolization, in melanocytes from the perilesional skin, and no autophagy was observed. The three stereological parameters were significantly different between the three groups of tissue specimens （all P < 0.05）, with the Nv, Vv and Sv of mitochondria being （7.194 ± 1.434） μm－3, （4.8 ± 1.2） %, （2.42 ± 0.86） μm－1 respectively in melanocytes from the healthy controls, （4.055 ± 0.906） μm－3, （7.4 ± 2.1）%, （3.58 ± 1.15） μm－1 respectively from patients with progressive vitiligo, （5.311 ± 0.873） μm－3, （6.5 ± 1.4）%, （2.82 ± 0.94） μm-1 respectively from patients with stable vitiligo. Conclusions Mitochondria are injured in melanocytes from perilesional skin of patients with vitiligo, and the degree of injury is more intense in progressive vitiligo than in stable vitiligo. 【Key words】 Vitiligo; Melanocytes; Mitochondria; Microscopy, electron, transmission