The changes and functions of mitochondria during the process of fertilization membrane(Fm)formation in Scylla paramamosain were investigated by transmission electron microscope.The results are as follows:Many mitochondria assembled densely at one place in the cortex just before the outburst of the ring-shaped granules.When exocytosis happened,numerous mitochondria scattered rapidly around the cortex where cortical reaction was proceeding.Mitochondria increased dramatically by splitting and budding,meanwhile lots of mitochondria that formed in endoplasm migrated to cortex,as numerous ringshaped granules involving exocytosis needed abundant energy.While Fm was swelling,most of the mitochondria gathered under the new plasm membrane to participate in its restoring and formation.After Fm swelled completely,mitochondria decreased suddenly and disappeared since cortical granules’ exocytosis had ceased.In short,the changes of mitochondria on its numbers,shapes and distribution,reflected the trait on physiological activation and energy supply in different stages of Fm formation.From the angle of the changes and functions of mitochondria,this study illuminated the mechanism of Fm formation on cellular level,and provided a new research field for Fm formation in Crustacea.