Asymmetric polyimide membranes were fabricated from casting solution of 18 wt% polyamic acid and 1.3-20 wt% additive agent in dimethylacetamide at 343 K, with 1 min evaporation time, followed by a cyclization process of thermal treatment in a bath of dioctyl sebacate under N-2 in three steps : 1 h at 373 K, 1 h at 473 K, 1 h at 573 K. The effect of additive agents and their quantity on the molecular weight cut-off (MWCO) performance of the asymmetric aromatic polyimide membrane were examined. By changing a sort of additive agents, the MWCO of the fabricated aromatic polyimide asymmetric membranes can be adjusted in the range of 400-650 daltons. By changing amount of additive agents, MWCO of the fabricated aromatic polyimide asymmetric membranes remain almost constant at the value of approximately 400 daltons for pyrene, and increased from 500-650 daltons for polystyrene.