The micropyle apparatus of eggs in the medaka, Oryzias latipes, was observed by scanning electron microscope.During the breeding season mature ova were fixed with 2.5%glutalaldehyde and 1%osmic-tetroxide for 1 hour each.After dehydra-tion with graded ethanol, the samples were dried with critical point drying, coated with platinum-palladium with ion sputtering, and studied with scanning electron microscope.The micropyle apparatus of unfertilized ovum in the medaka is composed of five or six spiral layers, becoming hollow in the central part.After fertilization, the cavity of micropyle was filled with a cluster of spherical substance.This substance increased over time.