Abstract. The concept of rotatability introduced by Box and Hunter (1957, Ann. Math. Statist., 28, 195-241) is an important design criterion for response surface design. Recently, a few measures of rotatability that enable us to assess the degree of rotatability for a given response surface design have been introduced. In this paper, a new measure of rotatability for second order response surface designs is suggested, and illustrated for 3 k factorial design and central composite design. Also a short comparison is made between the proposed measure with the previously suggested measures.