Abstract: Objective Marine Medaka (Oryzias melastigma) is a new marine model of biological toxicology. Methods In this study, the structure of the visual organ of marine medaka was observed, especially focused on variations of its eyeball and retina. Results The results were that the medaka’s visual organ developed very rapidly. At the embryonic period, the pigmented layer of the eyeball had appeared, and there already had a significant eye area. At the first day, the structure development of the eyeball and the retina were basically completed. At the 6th day, there was a significant difference of pigmented layer and photoreceptor layer between light and dark visuals. At 23th day, the retinal structure had greatly changed, which can explain the reason about the migration of medaka from the floating stage to the benthic stage. During from 9 to 14 month-old, the thickness of all layers in the retina decreased, indicating that the vision was degraded. Meanwhile, the kernel layer differentiation is obvious, as vertebral cells showed photoreceptor layer structure closely inlaid with rod cells, that O. melastigma has good light sensitivity and strong visual acuity. The visual organ’s rapid development of medaka can be recognized as it needs to adapt the surroundings and to keep the life events such as feeding. Conclusions The development process of the visual organs of marine medaka is obvious and can provide theoretical basis for further study of its behavior, and it can be a good experimental method for studying other related species.