Ketoprofen, 2-(3-benzoyl phenyl) propionic acid, has many advantages over the other antiinflammatory drugs, such as salicylates, phenytbutazone, and indomethacin. According to the reports, ketoprofen is well tolerated by patients and has very low incidence of side effects and toxic reactions. Although ketoprofen is widely used as an antiinflammatory agent, it shows poor solubility in water. In order to enhance water solubility, ketoprofen was made as lysine salt, such as acetylsalicylate lysine salt, ibuprofen lysine salt and amino acid salt of phenylbuatzone. The purpose of this study was to compare with ketoprofen lysinate in aspect of binding to human serum albumin (HSA) were made, and the association constant and the number of binding site were obtained using difference spectrophotometry. The number of binding site of HSA for ketoprofen and ketoprofen lysinate appears to be 3.3,3.2 respectively and association constants were found as follow; HSA-ketoprofen $2.23{ imes}10^4;M^{-1}$, HSA-ketoprofen lysinate $1.02{ imes}10^4;M^{-1}$.