The goal of this study is to deepen our understanding about how individual differences change over time when using ERP. Drawing on expectation-confirmation theory (ECT) and social cognitive theory, we develop a two-stage model and test it empirically by a longitudinal study. The proposed model considers whether confirmation and satisfaction drives the change of individual differences between usage stage and post-usage stage, and whether the modified individual differences in turn affect extended use of IS. We theorize individual differences as computer self-efficacy (CSE), computer anxiety (CA), and personal innovativeness in information technology (PIIT) and characterize complex IS as ERP implementation in Taiwan. The results of the 12-week longitudinal test based on 226 employees from 10 industries of Taiwan showed that modified individual differences and satisfaction affect extended use, and the original CSE and PIIT influence satisfaction. The results deepen our understanding about the change of IS users’ cognitions in the context where their volitional control over their behavior is limited and about the role played by satisfaction in changing their cognitions.