The olfactory rosettes of five species of Clupeiformes were studied by scanning and transmission electron microscopy. They are all oval in shape, consisting of 24-30 unfolded lamellae. Each lamella is composed of centrally located sensory epithelium encircled by marginal indifferent epi-thelium. In Etrumeus teres and Engraulis japonica, the sensory epithelium contains three types of cells, i. e., cells projecting 3-5 relatively long cilia radially from a round cell apex (type 2 ciliated cells), cells bearing a tuft of long microvilli (microvillous cells) and supporting cells provided with short microvilli. In Harengula zunasi, Sardinops melanosticta and Konosirus punctatus, cells bearing many cilia in a tuft (type 1 ciliated cells) are sparsely scattered in the sensory epithelium in addition to the above three cell types. Apical cytoplasm of supporting cells in Etrumeus is filled with large electron-lucent droplets.