A highly N-methylated cyclic heptapeptide, (-)-ternatin, was isolated from the mushroom Coriolus versicolor, which significantly suppressed fat accumulation against 3T3-L1 murine adipocytes (EC50 = 0.14 lg/mL). Although ternatin was previously reported to be antibacterial or antimicrobial compound, its inhibitory effect on fat accumulation has been first shown. The structure of (-)-ternatin was revised to be a cyclo [D-allo-Ile1 -L-(NMe)Ala2 -L-(NMe)Leu3 -L-Leu4 -L-(NMe)Ala5 -D-(NMe)Ala6 -(2R,3R)-3 hydroxy-Leu7 ] by spectroscopic analysis and chemical synthesis.