The eyes of the fly have been employed in an extensive range of studies, but the existence of diurnal rhythmicity, which is involved in the adaptation to different light environments between the day and night is still unclear. The rhythmicity of the photoreceptor cells of the blowfly Lucilia cuprina was observed over a precise time schedule under a daily light cycle. Both the morphology of the photoreceptive structure called rhabdom and the amount of the visual pigment chromophore were mostly constant. Each photoreceptor area measured from the cross sections and each amount of chromophore was ca. 22.5±1.85 μm² and ca. 1.4 pmol, respectively. The number of the multivesicular bodies, assuming the indicator of the photoreceptive membrane turnover, was small compared with other reports of arthropods. We confirmed that there is no diurnal rhythmicity either in the morphology of rhabdom or in the visual pigment contents under the daily light cycles.