The compositions of free phenolic acids in rapeseed flours of diverse origin and white mustard were highly variable but represented less than 10% of the total phenolic acids. Phenolic acids released from hydrolysis of soluble esters constituted the major fraction, with Polish varieties having higher levels than a Canadian variety or white mustard. Yellow Sarson contained low levels of phenolic acids. Sinapic acid isomers constituted over 94% of the 13 phenolic acids found in the rapeseed varieties. Only traces of several phenolic acids appeared to be structurally bound to rapeseed and mustard proteins and carbohydrates.