Abstract: The mass spectra of twenty four 1, 2-oxaborolanes derivatives have beendetermined and the mass spectrometric fragmentation pattern has been dis-cussed. For compounds 1～4, 2-aminoethoxy-, 2-methoxyethoxy-, 2-bromoe-thoxy-and 2-chloroethoxy-1, 2-oxaborolanes, the relative abundance of Mpeaks were correlated with different hetero-atoms, (N, O, Br and Cl). Be-tween borou and hetero-atom may be formed co-ordinate bond and inter-mo-lecular complex structure. Difficulty was encountered with determination ofthe mass spectrum of 2-phenyl-1, 2-oxaborolaue (12) due to its easy conver-sion to 2-pbenyloxy-1, 2-oxaborolane. The mass spectrum of compound (12)exhibited significant peak for ion m/z 91 C_7H_7~+, resulting from skeletal re-arrangement. The spectra of some 1, 2-oxaborolane and bis-(1, 2-oxaborolane)derivatives showed only weak molecular ions.