This study is to investigate factors that affect usage change in mobile data service (MDS). The central claim of this paper is that influencing forces of usage increase in MDS are different from those of usage decrease. We propose that information quality as the motivator (forces of usage increase) and system quality as the demotivator (forces of usage decrease) of MDS. A research model is proposed and subsequent hypotheses are empirically tested with partial least square (PLS) based on 478 responses from the users of mobile data service. We have found that information quality (as a motivator) is positively associated with usage increase in mobile data service, but system quality (as a demotivator) is not. Also, system quality is negatively associated with usage decrease, but information quality is not. Despite the recognized limitations, our study highlights the potential value of the two-factor theory in explaining user behaviors associated with mobile data services.