Stay-at-home orders and quarantines have not only shifted traditional face-to-face learning to online learning, but have also led to greatly increased consumption of digital devices during the coronavirus (COVID-19) pandemic. Thus, many students who were new to online learning were forced into a new environment. The purpose of this two-wave longitudinal study is to investigate the effects of internet addiction on online students' learning satisfaction during the COVID-19 pandemic. A total of two hundred and forty-nine undergraduate-level students from 51 of the 81 cities in Turkey completed an online questionnaire. The data used cross-lagged structural equation modeling. The results indicated that internet addiction at Time 1 decreased online students' learning satisfaction at Time 2. The results also revealed that online students' learning satisfaction (Time 1) did not affect internet addiction (Time 2). It is concluded that internet-addicted students had lower learning satisfaction in online learning environments. Thus, it is essential for institutions to provide effective online instruction, psychological coping tools, and social and behavioral support, which may help reduce internet addiction and minimize its negative impacts on online learning environments during the pandemic.