The ovary structure of ovoviviparous teleost, Swordtail Fish (Xiphophorus helleri), was observed using optical microscopy. Swordtail Fish egg development process was divided into six phases. Phase Ⅰ oocyte was in a primitive differentiation state, with clear plasma membrane. Phase Ⅱ oocyte was surrounded by a layer of follicular cells. Phase Ⅲ and Ⅳ oocytes differentiated significantly, with accumulated lipid droplets and yolk granules in the cytoplasm. Phase Ⅴ oocyte was a mature egg, with very thin egg membrane and rich lipid droplets and yolk in the cytoplasm. Phase Ⅵ oocyte entered the degradation stage, with protrusion of the follicular cells into the central oocyte, and yolk absorption. Follicular cells became hypertrophy. The results show that the oocyte development is not synchronous in the ovary of Swordtail Fish.