The mass spectra of diterpene orthoesters 1~12 derived from Daphne genkwa Sieb. et Zucc.(A),Daphne giraldii Nitsch.(B),Daphne tangutica Maxim.(C)and Wikstroemia chamaedaphne Meisn.(D)have been studied systematically.A detailed comparison of the spectra of analogous series,high resolution mass spectral data and metastable measurement by defocusing technique allowed the structure-spectral correlations to be generalized as follows: (1)12-OCOR′ analogs(2~4,6,8,9)dominate by the loss of the 12-substituent leading to the formation of(M-R′CO_2~·)and(M-R′CO_2H)peaks,which then furnish the skeletal ion m/z 358 through further elimination of RCO_2H+H~· or RCO_2H~·,while the 12-OH analogs(1,7)will give M-H_2O,M-H_2O-RCO_2H(m/z 358)in a similar way. (2)Members carrying no substituent at 12-C(10~12)exhibit even-mass peak at m/z 360 (M-RCO_2H),accompanied sometimes by a less pronounced peak at m/z 358.(3)Members with free 20-OH group show significant (M-~·CH_2OH)and(M-~·CH_2OH-H_2O)peaks, while the acylated derivatives(20-OCOR″)tend to provide M-(R″-H)CO via 4-mem- bered transition intermediates.(4)The presence of particular ester or orthoester groups at 12-C or 21-C may easily be identified by the acylium ions(R′CO~+ or RCO~+)at the low mass region.In most cases conjugated acyliums are displayed as strong or base peaks. (5)m/z 358,340,327,322,317,311,299,281,271,253,...as well as ion series with 2u mass increments at m/z 360,342,329,324,319,313,301,283,273,255,...may serve as an indication of the presence of diterpene skeleton bearing either OH,OCOR′ or H at 12-C,respectively. Based on the fragmentation mechanism so far reached,the structures of three new analogs 5,6,and 13 were thus assigned as tanguticacine,daphnegiraldin and 15,16- dihydrodaphnetoxin,respectively.