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This dissertation is composed by two parts. The first part reports the phytochemical investigation of two Tibetan medicine plants, Daphne tangutica Maxim and Euphorbia wallichii Hook. f. F1. Sixty different compounds including ten new compounds and two novel diterpenoids possessing a new carbon skeleton were isolated and identified. The second part is a review about the progress of studies on the polycyclic diterpeniods of the plant family of Euphorbia.The first part consists two chapters, which expatiate on the isolation and identification of chemical constituents from D. tangutica and E. wallichii.Thirty-one compounds were isolated from the root barks of D. tangutica by methods of column chromatography (silica gel, including reversed phase), preparative TLC and HPLC, and their structure were identified as nine daphnane diterpenes, six lignans, nine cumarin derivatives, five phenylpropanoid derivatives, a steroids and a benzoate on the basis of spectroscopic methods including IR, MS and NMR. Among them, three are new diterpenes with skeleton of daphnane and the structure were determined as 1,α-dihydro-20-palimoyl-daphnetoxin, 1,2α-dihydro-5β-hydroxy-6α,7α-epoxy-resiniferonol-14-benzoate and 1,2β-dihydro-5β-hydroxy-6α,7α-epoxy-resiniferonol-14-benzoate. In addition, thirteen known ones were isolated from this plant for the first time.Isolation of the roots of E. wallichii yielded thirty compounds, twenty-four of
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