Different gestational age fetal follicles of Northeast China Fine-fleece Sheep were histologically studied. The results showed that boundaries between medulla and cortex was ambiguous at the eighth week and became obvious at the twelfth week. Primordial follicles could be found in 8-week fetal ovaries and some follicle cells became irregular cuboid in 12-week, but primary follicles could be found until 16-week. There was significant difference between 8-week and 12-week follicles in size (P＜0.01), most mitochondria were round, some diamond, irregular and juvenile ones could be found with the development of oocytes. Some of oocytes degenerated in each stage of development. The diameter of primary oocytes, primordial follicles and primordial follicular oocytes were larger in 12-16 weeks fetal ovaries than other times.