Previous studies on the relationship between corporate governance and earnings management have shown different results. This study explores how market power and industry competition influence the effect of corporate governance on earnings management in Taiwan. Industry competition is an industry-level measure for the competition among firms. Firm market power is a firm-level measure for the power to compete with external competition. We discover that firms with low market power and those faced with intense market competition are more likely to engage in earnings management. Market power demonstrates a more significant effect than industry competition on managerial earnings manipulation. Moreover, when market power is weak or industry competition is fierce, corporate governance cannot mitigate earnings management. Regression results considering the interaction between market power and industry competition reveals a stronger effect of corporate governance on earnings management than those evaluated based on market power or industry competition alone. Our findings provide a possible explanation for the different relationship between corporate governance and earnings management.