Transgenic components in genetically modified organisms consist not only of the transgenic genes， but also the transgenic protein. However， compared with transgenic DNA， less attention has been paid to the detection of expressed protein， especially those degraded from genetically modified soybean after food processing. In this study， the full length 5-enolpyruvyl-shikimate-3-phosphate synthase (CP4-EPSPS， 47.6 kD) protein was probed with the SC-16 (S19-R33) and the DC-16 (D219-K233) polyclonal antibodies in immunoblots. Both antibodies were able to detect the full length CP4-EPSPS and its residues in soy powder made from Roundup-Ready soybeans after heating and microwaving treatments which also reduced the molecular weight of the protein to 45.8 and 38.7 kD， respectively. Taken together the immunoblot results suggest that the middle region of the CP4-EPSPS protein possessed better stability than its N-terminal during thermal processing. This deduction was further validated by autoclave treatment， where a 37.4 kD residue of the protein was recognized by DC-16. A similar result was obtained in processed smoked sausage containing Roundup Ready soybean protein isolate (as an extender). The additional use of a further polyclonal antibody CK-17 (C372-K388)， showed that compared with only the one signal for CP4-EPSPS detected by the SC-16 and CK-17 antibodies， the DC-16 middle region antibody detected four signals for CP4-EPSPS from five market sourced soy protein concentrates. Taken together， the study suggested that the middle region of CP4-EPSPS was more useful than the N- and C-terminal for tracing transgenic CP4-EPSPS protein and its remnants in highly processed soy-related products.