Two single chain protein-biosynthesis inhibiting Proteins: Luffin-A and B were isolated from the seeds of Luffa cylindrica. Luffins were extracted from defatted meal of the seeds at PH 7.2, fractioned by ammonium sulfate precipitation, and then aPPlied to CM-52 ion-exchange chromatography. SephacrylS-100 gel filtration and ion-exchange FPLC. Luffin-A. B are basic proteins with isoeleetric points of about 10 with molecular weights of 27kd and 28kd respectively.Although their amino acid compositions Showed them to be homogeneous Proteins,their immunogenities as judged by double-diffusion and ELISA indicated some difference. Luffins exhibit potent inhibition of protein synthesis in rabbit reticulocyte lysate. IC50 are 1 .4×10-11 M and 2 .0×10-11 M respectively, which are muchlower than that of TCS (2.9×10-10M), It is promising that Luffins may be used asan efficient toxin moeity of immunotoxins.