One of the factors that determines the nutritive value of fishmeal as a protein concentrate for ruminants is its ruminal degradability, which varies with processing methods. It is possible that this variation could be related to the chemical modification of the amino acids/protein or to the change in protein solubility during the industrial processing. The objective of this work was to examine the effect of heat treatment of fishmeal on its ruminal degradability, protein solubility and the oxidation state of methionine.