ABSTRACTSoy protein hydrolyzate (SPH) was investigated to identify the phenolic compounds responsible for antioxidant activity. Three isoflavones–genistein, daidzein, and glycitein–were found in SPH. These are the same isoflavones that have been identified in raw soybeans. No isoflavone glycosides were found in SPH. The phenolic acids found in SPH were caffeic, ferulic, p‐coumaric, syringic, vanillic, gentisic, and p‐hydroxybenzoic acids. The compounds were identified by TLC, GLC and UV spectra. The isoflavones were confirmed by their mass