Recently, Yeh et al. pointed out that the enhanced version of the generalized password-based authenticated key agreement protocol proposed by Kwon and Song is insecure against the off-line password guessing attacks. But, Yeh et al. did not propose an improved version of Kwon and Song's protocol. Therefore, this paper proposes an improvement of Kwon and Song's enhanced version that can withstand various crypto graphical attacks and provide same efficiency.