Microsporidian spores were isolated from yellow-hind winged arctiid, Eilema griseola (H?bner), and cutworm, Agrotis tokionis Butler, and their morphological characteristics and their infectivity to silkworms were investigated. The shape of the microsporidian isolates was oval and the sige of the spore isolated from yellow-hind winged was measured in 2.6 X1.5μ and that of the isolated from cutworm was measured in 3.7×2.0μ. Both the isolated microsporidians showed the infectivity to silkworms, but the isolate derived from rice leaf beetle did not infect silkworms. However, none of the isolates did transovarian transmission in silkworms and the silkworm moth infected with the isolate from yellow-hind winged laid eggs irregularly.