In this article, we discuss the effects of amino acids on amyloid aggregation of lysozyme. l-cysteine (Cys) dramatically inhibited fibrillation of lysozyme, whereas other amino acids (including l-arginine) did not. In the presence of Cys, the aggregation pathway of lysozyme shifted from fibrillation to the formation of the small worm-like aggregates with unfolding. The interaction between Cys and lysozyme was observed to be non-covalent, suggesting that the thiophilic interaction between the thiol group on the side chain of Cys and the core sequence of lysozyme significantly contributes to the inhibition of amyloid aggregation. These findings provide a new basis for the design of a biocompatible additive to prevent amyloid fibrillation. (c) 2014 American Institute of Chemical Engineers Biotechnol. Prog., 30:470-478, 2014