This report describes the inhibition of the proteolytic activity of Haemonchus contortus lysate by a mixture of n-alkyl ferulates isolated from Maprounea guianensis. These compounds were evaluated in vitro for the ability to inhibit the H. contortus proteases using SDS-PAGE copolymerized with gelatine (zymography) and by assaying the hemoglobinolytic activity of these enzymes in solution. The ferulates abrogated the proteolysis compared to E-64, suggesting the activity is the result of a cysteine protease.