In　order　to　gain　deeper　insight　into　the　interaction　mechanism　between　bovine　serum　albumin　(BSA)　and　polyethylene　glycol　(PEG),　the　present　work　applied　elastic　light　scattering　(ELS)　spectroscopy　to　investigate　the　interaction　between　BSA　and　PEG,　and　explore　the　effects　of　concentration　and　molecular　weight　of　PEG　on　the　interaction　at　physiological　pH.　The　results　showed　that　the　interaction　force　existed　between　linear　PEG　and　spherical　BSA　molecules　was　mainly　hydrogen　bonding.　In　addition,　the　apparent　binding　constant　of　system　was　evaluated　by　model　calculation.　©　(2013)　Trans　Tech　Publications,　Switzerland.