Earnings information plays a very important role in firm valuation. Investors typically use current and past earnings to predict future profitability and risk, and apply them to valuation models to estimate firm value. If investors face information uncertainty due to lack of earnings precision in firm valuation, they are likely to rely on additional information to resolve information uncertainty in earnings signal. This study examines whether insider purchase transactions after the announcement of quarterly earnings resolve the uncertainty regarding the earnings signal by providing information about the persistence of the previously reported earnings. If the insider purchase transactions provide useful information for resolving the uncertainty of the past quarterly earnings, the market reactions to the insider purchase transactions are expected to have a significant association with the uncertainty about earnings and the changes in previous quarterly earnings. Our sample consists of 12,318 insider purchase trades disclosed by KOSPI and KOSDAQ listed firms over the 2002-2015 period. For the KOSPI listed firms, we find that the market reactions to insider purchase transactions increase with information uncertainty about earnings signal measured by accruals. This indicates that information contents of insider purchase transactions increase with information uncertainty in earnings signal. In addition, when the previous quarterly earnings changes before insider purchase trading are positive, there is a significantly positive relationship between the earnings changes and the market reactions to insider purchase disclosures. This is consistent with insider purchase transactions confirming earnings signal of the previous quarter. The results also reveal that insider purchase trades for the KOSPI listed firms mainly provide private information regarding the past quarterly earnings changes, whereas the literature on insider trading shows that insider purchase trades convey management private information about future earnings prospects of the firm. In contrast, insider purchase trades for the KOSDAQ listed firms provide neither information about the past quarterly earnings changes nor information about future earnings. Our study expands the literature by focusing the confirmation role of insider purchase trading. Our results provide useful insights for better understanding of the information conveyed by insider purchase transactions in Korean capital markets.