This paper presents the observation on the structure,quantity,distribution andmembrane characteristics of mitochondria in spermatogonia,spermatocyte,spermatidand mature sperm during spermatogenesis.They were examined by electron micro-scope (ultrathin section and freeze fracture).Conclusions obtained are as follows:1.There exists regular changes for the proliferation,development and distribu-tion of mitochondria.(a)Quantity of mitochondria:total number of mitochondriain spermatogonia are 80-120 for one cell.They increase to 400-500 in primary sper-matocyte.Spermatid has 200-300 mitochondria.(b)Distribution of mitochondria.Mitochondria in spermatogonia distribute randomly.There are several groups ofmitochondria in spermatocyte.During spermatogenesis mitochondria moved fromhead to back side.In Golgi phase and cap phase spermatid,mitochondria situatedunder the plasm membrane,in mature sperm they arrange regularly outside the densefiber of middle piece of tail.(c)Structure and development:Mitochondria inspermatogonia are round and oval.Cristae arrange parallelly.At spermatocyte stagemitochondria are proliferated by dividing itself.Newly formed mitochondria haveno cristae.In mature sperm mitochondria developed well,but arrangement ofcristae is not regular.2.Membrane of mitoehondria.There are three laminar structure for mitochon-drial membrane.It is thinner than plasm membrane.Protein particles in outermembrane are more than inner membrane.There are a few protein particles in cristae.3.The changes of mitochondria have close relationship with spermatogenesis.(a)Mitochondria proliferate itself rapidly in spermatocyte to match with enlarge-ment of cellular size and content:(b)Mitochondria situated near the Golgi complexin Golgi phase spermatid,after cap formation they moved to tail side to support thetail formation.(c)In mature sperm mitochondria arranged regularly in middlepiece,so sperm can swim quickly.