Baldesar Castiglione was one of the most fascinating figures symbolizing the change in the humanistic culture of the early Cinquecento Italy. Also his highly acclaimed work, Il libro del Cortegiano, has been regarded as a literary representation which displays a cultural tension of the Renaissance between idealism and realism. The present study is an attempt at interpreting him and his book as the grids with which one can fathom such change and tension within a larger political context of Renaissance court society. In particular, by scrutinizing the virtues of the ideal courtier which Castiglione suggested in the work, this study puts its main focus upon the question of how the Renaissance constructed a new concept of man. For this purpose, the study begins with the thorough analysis of two important concepts appearing in the work: first, grazia, the ultimate end of courtier’s behavioral ethics; second, sprezzatura, the aesthetical mode of courtier’s behavioral practice. Taking this interpretation of grazia and sprezzatura into serious consideration, both become politico-ethical concepts which may find their places within social relations. The next chapter deals with the relationship between the courtier and his princes. It is beyond doubt that prince was the center of Renaissance court; all of courtly lives and values revolved around him. In that small world, courtier was nothing but an artificial being sealed in and fashioned by the power relationships. Based upon what were discussed hitherto, the final chapter maintains that the image of the ideal courtier who Castiglione portrayed was that of flexible and mutable social being, far from the spiritual one who Burckhardt emphasized as the prototype of modern individuals.