Two new isosteroid alkaloids, N-methyl-22,26-imino-13,22-oxido-5 alpha, 20 alpha-jervine-3 beta-ol-6-one, pengbeimine B (1) and N-methyl-22,26-imino-13,22-oxido-5 alpha, 20 beta-jervine-3 beta-ol-6-one, pengbeimine D (2) were isolated from the fresh bulbs of Fritillaria monatha Migo. Their structures were determined by spectral methods, and were proved by X-ray diffraction.