This dissertation mainly presented the investigation of natural products from two different Formosan gongonian soft corals, Briareum violacea and Junceella fragilis. Their extracts were examined by intensive chromatographic methods. Eighty-four compounds including fifty new briaranes were isolated, and parts of their biological activities were studied. Natural products investigation of the Taiwanese gorgonian octocoral Junceella fragilis found fifteen new briarane-type diterpenes, namely frajunolides E-S (1-15), ninteen known briaranes, eg. junceellin, junceellolides A-E¡Bjunceellolide K, 11£\,20£\-epoxy-4-deacetoxyjuncellolide D, umbraculolide A, junceellonoid A, juncin P, juncins Y-ZI, frajunolides A-D and praelolide, and a sterol, ergosterol peroxide. Soft coral B. violacea (Quoy and Gaimard) of Taiwan has isolated thirty-five new briarane-type diterpenoids, briaviolides A-Z (16-41) and viobrianolides A-I (42-50), in addition to fourteen known diterpene lactones, stylatulide lactone, excavatolide A, 9-deacetylstylatulide lactone, 4£]-acetoxy-9-deacetylstylatulide lactone¡B Brianthein Z¡B, renillafoulin A, braexcavatolide E, braexcavatolide I, minabein-4, minabein-6, milolide K, solenolide A, and solenolides D-E. Structures of all above compounds were examined by physical and spectroscopic analyses including mass, IR, UV spectra, optical rotation and 1D, 2D NMR, as well as in comparison with the published data. Moreover, the structures of compounds 16, 32 and prarlolide were further confirmed by single X-ray crystallographic analysis. The stereochemistry of these compounds was investigated by NOESY method, and the configuration of compounds 32-38 were determined by Circular Dichroism spectroscopic analysis. Cytotoixcity and in vitro anti-inflammatory activities were studied by Dr. Kuo, Yao-Haur and Dr. Hwang, Tsong-Long, respectively. Junceellin, junceellolide B and juncin ZI exhibited weak cytotoxicity against Hep2 (Human laryngeal carcinoma), Doay (Human medulloblastoma), WiDr (Human colon adenocarcinoma), Hela (Human cervical epitheloid carcinoma). The in vitro anti-inflammatory activities of 1-7 were evaluated for inhibition of elastase release and for the generation of superoxide anion, as tested on human neutrophils. Compounds 1 and 6 exhibited weak inhibition of elastase release and superoxide anion at 10 £gg/mL. The biological activity analysis of compounds 16-50 are in progress.