This study examines the effectiveness of accounting conservatism in monitoring and controlling managers’ decision-making regarding opportunistic investment. We find that accounting conservatism is negatively associated with over-investment. This suggests that conservative accounting policies serve as an efficient monitoring and controlling mechanism for opportunistic investment decisions. We also find a stronger negative association between accounting conservatism and over-investment in firms with low managerial ownership and low ownership by foreign investors. The results of our analysis imply that the impact of timely loss recognition on over-investment is more significant in firms with high agency problems and weaker monitoring ability, ...