The structural information of protein molecules on solid phase, such as conformation and orientation , has attracted much attention. In this report, we try to evaluate structural change of proteins via measurement of the adsorption amount of non-ionic detergent (TritonX-100) to proteins immobilized covalently on the matrix surface by a surface plasmon resonance (SPR) sensor. The adsorption amount of detergent to alpha -glucosidase and apomyoglobin is dependent on the amount of immobilized proteins and their surface net hydrophobicity. Moreover, it is observed that the adsorption amount of detergent to proteins increases in proportion to the denaturation degree of proteins induced by 6M guanidinium chloride solution. Consequently, it is revealed that measurement of the adsorption amount of detergent to proteins is applicable to detecting conformational changes of proteins on solid phase.