This paper aims to investigate the association between earnings management and investment efficiency. This study further examines the moderating role of information uncertainty in this relationship. Based on an analysis of 536 Vietnamese listed firms from 2010 to 2022, the findings reveal a positive relationship between earnings management and investment inefficiency. Furthermore, the findings indicate that firms with higher levels of information uncertainty exert a stronger influence on the relationship between earnings management and investment efficiency. The findings support the agency theory that when there is high information uncertainty (i.e., accentuating information asymmetry issues), managerial opportunistic behavior via earnings management can result in the problem of under and over-investment. To the best of the authors’ knowledge, this paper is the first to investigate the moderating influence of information uncertainty on investment efficiency.