The cationic polymerization of 2-methylaziridine using boron trifuoride etherate as initiator at different monomer/initiator ratios, temperatures, solvents, and times of polymerization was carried out. The effect of these variables on the polymerization yield and viscosity of the polymers was studied. All the polymers were characterized by elemental analysis, FT-IR, H-1-NMR, C-13-NMR spectroscopy, thermogravimetric analyses and differential scanning calorimetry.