Abstract: A Series of alkaloids isolated from SOPHORA ALOPECUROIDES L. were shown to have quinolizidine skeleton. This paper summarizes the MS patterns of matrine, sophoridine, sophocarpine, sophoramine, oxymatrine and lehmannine using high resolution and metastable ion measurements. The results show: (1) All of these compounds reveal the molecular ions to be usually base peak or second strong peak. (2) The stronger ions of m/z 150, 148, 137, 136 containing ring A and B are produced via ring C cleavage. (3) Ring A gives rise to stronger ions m/z 98, 96. The above results mainly from induction of the free radical N. The MS differences of these compounds depend on their configurations, the position of the double bond and the presence or absence of N→O.