Six dihydrobenzofuran type neolignans were isolated from the dried ripe seeds of Myristica fragrans Houtt. (family: Myristicaceae) and their chemical structures were identified as licarin B (1), 3'-methoxylicarin B (2), myrisfrageal A (3), isodihydrocainatidin (4), dehydrodiisoeugenol (5), and myrisfrageal B (6), respectively, on the basis of spectroscopic data analyses. Among them, compounds 3 and 6 are new compounds. Compounds 1-6 showed inhibition of nitric oxide production in lipopolysaccharide-activated murine monocyte-macrophage RAW264.7 with IC50 values of 53.6, 48.7, 76.0, 36.0, 33.6, and 45.0μM, respectively. These values were compared to those of the positive controls, indomethacin and L-N(6)-(1-iminoethyl)-lysine, which have IC50 values of 65.3 and 27.1μM, respectively. Further compounds 3, 5 and 6 suppressed LPS-induced iNOS mRNA expression in a does-dependent manner in RAW 264.7 cells assayed by real-time RT-PCR. Compounds 3, 5 and 6 may inhibit NO overproduction via inhibition of iNOS mRNA expression. The results provided valuable information for further investigation of compounds 1-6 as anti-inflammatory and chemopreventive agents.