In this article, we deal with the investigation into a poly(lactic acid) (PLA) preparation process catalyzed by a non-metal-based compound. Low-molecular-weight PLA was synthesized by the direct melt polycondensation of L-lactic acid catalyzed by methanesulfonic acid (MSA). This study was focused on the investigation into optimal MSA concentration determination and into the temperature (130, 145, 160, 175, and 190 degrees C) and time (6, 12, 18, and 24 h) influence on the structure (Fourier transform infrared spectroscopy), molecular weight (viscometric measurements and gel permeation chromatography), and thermal properties (differential scanning calorimetry) of the samples. The results show an optimal MSA content of 0.5 wt %. The highest molecular weight of PLA prepared by this method was reached after 18 h of reaction at 175 degrees C (weight-average molar mass = 17.2 x 10(3) g/mol). (C) 2010 Wiley Periodicals, Inc. J Appl Poly m Sci 116: 1597-1602, 2010