This study aimed to explore the impact of melatonin (MLT) on the ultrastructure of oocytes in preantral follicles of Vulpes fulva during the anestrus stage. Five left side ovaries for each group were collected from seven month old healthy MLT implanted or non-MLT implanted Vulpes fulva, respectively. The ultrastructures of 1-5 follicles from different stages in each ovary were examined by transmission electron microscope. A few mitochondria and golgi apparatus in primordial follicles were detected in both MLT implanted and non- MLT implanted Vulpes fulva. A small amount of smooth endoplasmic reticulum was found only in the primordial follicles of non- MLT implanted Vulpes fulva. Zona pellucida started to form in primary follicles with a few of cortical granules along the zona pellucida. And the number of mitochondria and endoplasmic reticulum increased in primary follicles in both groups. The number of zona microvilli in secondary follicle oocytes of non- MLT implanted Vulpes fulva was greater than that of MLT implanted Vulpes fulva. The results suggest that MLT only impacts the development of endoplasmic reticulum in Vulpes fulva primary follicles at anestrus stage.