Abstract: AIM　To investigate the fragmentation behavior of three 4(20)-methylene 5/7/6 type taxoids, and the influence of types and positions of the substituents on fragmentation. METHODS　The CID-MS/MS spectra of adduct ions such as ［M+H］⁺ and ［M+Na］⁺ were measured by FAB, as well as some related characteristic ions. In addition, the high-resolution data of characteristic ions were determined. RESULTS　The loss of HOBz is the major mode of decomposition of ［M+Na］+ ion for compounds 1 (brevifoliol) and 2 (taxchinin A), while ［M+H］⁺ ion of 3 (7-acetyl-10-deacetyl-7-debenzoylbrevifoliol) mainly undergoes the decomposition reactions of expelling one or two H₂O molecules. After loss of all AcO and BzO and some OH groups, 1 and 3 produce fragment ion with stable conjugated system at m/z 237, and 2 at m/z 253. CONCLUSION　The related compounds with slight structural difference can be effectively differentiated using MS/MS technique.