This research, draws upon an integrative model of IT business value, examines the mediating effect of an "IT organizational assimilation capacity" between IS integration and organization competitive advantage. Using a large-scale sample survey where responses were obtained from CIOs and senior business executives, we provide robust evidence of the "IT organizational assimilation capacity" mediating role. An interesting result of this research shows that the firm size was not found to be of significant influence. The implications of these findings extend the boundary of current literature on the dynamics of IT business value and contribute theorybased conceptual synthesis and empirical evidence to an IT/IS literature.