Cultivation characteristics of fruit-body (synnema) formation of Isaria japonica were examined using liquid and solid media in order to produce fruit-bodies on a large scale. Mycelia grew well at 18–28°C on PDA medium with an initial pH of 7.0. The formation of fruit-bodies of I.japonica was induced by lowering temperature to below 20°C in PD liquid medium. In sawdust-rice bran basal medium mixed with pupal powder prepared from silkworms (Bombyx mori), the fresh weight of fruit-bodies increased with increasing content of pupal powder. The highest yields of fruit-bodies were obtained in carbon-rich barley grain medium supplemented with pupal powder. The fruit-bodies grown under CO 2 concentrations of 1,000μl/L had coral-like, many-branched synnemata with numerous conidiospores, whereas those formed under high concentrations (9,000μl/L) of CO 2 had unbranched and longer synnemata. High concentrations of CO 2 remarkably inhibited conidiospore formation on synnemata. Continuous high-intensity illumination at 2.93Wm -2 inhibited the elongation of synnemata, and low-intensity illumination at 0.088 Wm -2 slightly inhibited the branching of synnemata. Fruit-bodies were produced on the pupa metamorphosed from living larvae of Agrotis fucosa placed on the surface of a culture of I. japonica incubated in sawdust-rice bran medium.