Six new compounds, irciformonins E~J (1~6), were isolated from CH2Cl2/MeOH extract of the sponge Ircinia formosana collected in Taiwan, toghther with two known compounds, irciformonins A and B. These compounds possess a linear C-22-sesterterpenoids type skeleton. The structures of all compounds were elucidated by spectroscopic analysis including 1D and 2D-NMR, optical rotation, IR, UV and high resolution mass spectra, as well as comparison with those in references. The stereochemistry of these compounds were determined by NOESY experiments, MM2 minimized energy, as well as comparison with those in references. The structures of all compounds possess a furan ring, a five membered lactone ring , and three methyl groups. Compounds 1 and 2 are geometric isomers. The differences between them are the substituents of the methoxyl group and the double bond. Compounds 1 and 2 possess substituents of the methoxyl group at C-10 and C-12 and have the double bond at C-11/C-12 and C-10/C-11. The differences between compounds 3 and 6 are the functional groups of the acetyl moeity and the double bond. Compound 3 has an acetyl group at C-12. Compounds 3 and 6 contain two double bonds at C-10/C-11 and C-11/C-12. Compound 4 has a cyclopentane between C-12~C-15 and a ketone group at C-10 while compound 5 possesses two acetyl groups at C-10 and C-15 positions.