A polymeric catalyst, polyaniline-sulfate, was studied in the transesterification of triglycerides (triacetin, castor oil) and esterification of fatty acid. ricinoleic acid with methanol at mild conditions (temperature of 50-60 degrees C). Polymer powder (PANI-S) and three samples of various contents of polymer deposited on carbon support were examined. The samples of catalysts, before and after catalytic tests were characterized by BET, FT-IR, XRD and SEM techniques. The acid capacity was also determined. All the samples were found to be active solid acid catalysts in both tested reactions. Catalytic performance of polyaniline-sulfate-based catalysts for methanolysis of triacetin (glycerol triacetate) the shortest triglyceride molecule differed from that for vegetable oil, castor oil, consisting of long chain triglycerides of ricinoleic acid. In transesterification of triacetin PANI-S powder was more active than carbon-supported catalysts. In methanolysis of vegetable oil the outermost surface of catalysts was mainly involved and much higher activity was exhibited by carbon-supported catalysts with deposited polymer, especially with low content of polymer (13.1 wt.%). The activity of polyaniline-sulfate-based catalysts was almost stable during recycling use in tested reactions. After five successive catalytic runs, their activities were found to be ca. 80-95% relative to the activities of fresh catalysts. (C) 2010 Elsevier B.V. All rights reserved.