The structures of the egg envelope in fertilized eggs of three species of characidae, head and tail light fish (Hemigrammus ocellifer), black tetra (Gymnocorymbus ternetzi), and buenos aires tetra (Hemigrammus caudovittatus) were studied using light and electron microscopes. The fertilized eggs in all species were colorless, transparent, spherical and non-floted type. The egg envelopes have a single micropyle resembling the pathway of sperm in the area of the animal pole. The micropyle was surrounded by protruded lines of the egg envelope in a radiated form. Egg envelopes of fertilized eggs in both head and tail light fish and buenos aires tetra consisted of three distinct layers; an outer layer, a middle layer and an inner layer. And that of blacktetra consisted of two layers; an outer layer and an inner layer. Also, an outer layers of both head and tail light fish and black tetra were adhesive types but, in that of buenous aires tetra was non-adhesive type. An outer surface of egg envelope in black tetra was arranged by pores regularly. In that of head and tail light fish and buenos aires tetra have a rough side. An inner layer of egg envelope in fertilized eggs consisted of lamellae alternating with interlamellae of lower electron density; an inner layer of fertilized eggs in head and tail light fish consisted of three layers, that of black tetra was four layers, and that of buenos aires tetra was five layers.