Poly(β-alanine) was successfully synthesized by an alternative method, which is the direct polyamidation of β-alanine in ionic liquids with triphenylphosphite as a condensing agent. It was found that 1,3-dimethylimidazolium dimethylphosphate was the most suitable reaction medium, in which a number-average degree of polymerization up to 49.5 was obtained. It was shown that the method is also applicable to the direct synthesis of polypeptides, for example, poly(l-valine) and poly(l-isoleucine).