Through the lens of rational addiction theory (Becker and Murphy, 1988), this study investigates whether addiction to mobile social apps should be viewed as a rational behavior rather than an uncontrollable, irrational disorder. To derive the analytical model, this study extends the rational addiction framework to include a utility-level network effect as the key factor that regulates the inter-temporal consumption of mobile social apps. Further, to validate empirically the rational addiction model in this context, we gathered and analyzed longitudinal panel data on the weekly app usage of thousands of smartphone users. The findings suggest that consistent with the rational addiction theory, users of mobile social apps are rational and forward-looking. They determine their current consumption based on both past and future consumption and the utility derived from network effects. However, the extent of rational addiction to mobile social apps varies considerably across diverse demographic groups and app categories.