Polymer-based solid acid catalyst, polyaniline (PANI) salt, is used for the first time to synthesize polymer. In continuation of our work to synthesize organic chemicals using PANI-based solid acid catalyst, in this work, polylactic acid is synthesized by the condensation polymerization of lactic acid using PANI salts. PANI salts are characterized by FTIR, FE-SEM, and TGA analyses. Polymerization of lactic acid in xylene solvent at 140°C for 24 h with the use of very low amount of PANI catalysts gave polylactic acid (PLLA) in the order: PANI-MSA (46%) > PANI-TFA (33%) > PANI-Bi(OTf)3 (27%) > PANI-Cu(OTf)2 (20%) > PANI-Yb(OTf)3 (15%). Molecular weights of PLLA synthesized using PANI-MSA and PANI-TFA are found to be 4385 and 4830, respectively. This methodology gives highly crystalline polymer with mushroom cap-like morphology. Advantage of this methodology is the use of easily synthesizable, recyclable, easily handlable, cheaper, and eco-friendly nature of the catalyst. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41147.