Ferulic acid (feruloyl) esterases are a novel subclass of the carboxylic acid esterases, and are able to hydrolyze esterified phenolic acids from plant cell walls. The active sites of feruloyl esterases show high homology with the serine active sites of lipases, and a model of a feruloyl esterase (FAE-III) from Aspergillus niger was derived based on the structure of four lipases. Stability of this feruloyl esterase was compared to a feruloyl esterase from A. tubingensis using chemical and thermal denaturation. These enzymes show a 92.5% identity in their amino acid sequences. The A. tubingensis feruloyl esterase is more sensitive to degradation than the A. niger FAE-III. These enzymes have potential in the food and agro-chemical industries.