From a MeOH extract of the aerial part of Piper futokadsura, the tetrahydrofuran lignans, futokadsurin A [(7S,8S,7S,8R)-3,4,3-trimethoxy-4-hydroxy-7,7-epoxylignan], futokadsurin B [(7R,8R,7R,8S)-3,4-dimethoxy-3,4-methylenedioxy-7,7-epoxylignan], and futokadsurin C [(7R,8R,7S,8S)-3,4-methylenedioxy-3,4-dimethoxy-7,7-epoxylignan] were isolated, together with nine known neolignans. In addition, L-tryptophan, pellitorine, phytol, elemicin, and 1,2,4-trimethoxyphenyl-5-aldehyde were isolated. The structures of the new compounds were elucidated using spectroscopic methods. These lignans inhibited nitric oxide production by a murine macrophage-like cell line (RAW 264.7), which was activated by lipopolysaccharide and interferon-g.