The detailed phenotypic analysis of a Drosophila melanogaster mutant, designated Frd, which was isolated for retinal degeneration phenotype was performed by examination of pseudopupil, electron microscopy, and electroretinogram(ERG). The photoreceptor cells of homozygous mutant degenerate right after eclosion. The retinal degeneration of the heterozygous mutants is slower than that of the homozygous mutants(it starts about one or two days after eclosion. The electron microscopic analysis of the heterozygous mutant showed that the retinal degeneration starts with the destruction of the rhabdomere structure where the initial response to the light stimulus occurs. Furthermore, the retinal degeneration is accelerated by the light, suggesting that the corresponding gene encode the protein directly involved in visual signal transduction. The ERG profile of the mutant suggests some level of defects in photoreception of the mutant, which is independent of the retinal degeneration phenotype. Further analysis of the mutant using various genetic and molecular biological techniques will help the understanding of the similar genetic diseases of the animals, particularly Retinitis pigmentosa in human.