Prior research finds that firms in the KOSDAQ market tend to manage annual earnings more than their counterparts in the KOSPI market. However, there is little research that systematically investigates differences in quarterly earnings management between the two groups. Hence, this study examines whether there are differences in quarterly earnings management between KOSPI and KOSDAQ firms. We also examine whether accounting reforms adopted to improve the quality of financial statements are effective in restraining quarterly earnings management. The results reveal that the KOSDAQ firms manage quarterly earnings to the greater extent than the KOSPI firms. We also find that the IFRS adoption has positive effects on quarterly earnings management in both KOSPI and KOSDAQ markets, whereas the auditor review of interim financial statements has no effect on quarterly earnings management.