The measurement issues inherent in Basu's asymmetric timeliness model, which is widely used in research on accounting conservatism, have been extensively noted by numerous international researchers. However, studies that intensively examine the problems arising from the estimation of the Basu model in the Korean context are extremely rare. Given the claims in the accounting and finance literature that the informativeness of accounting earnings and stock returns—the key variables of the Basu model—is affected by country-specific characteristics, re-examining the problems arising from the estimation of the Basu model using Korean firm samples is essential for ensuring the validity of empirical research on conservatism in Korea. The empirical analysis of this study found that the estimation bias problem of the Basu model also exists in Korean firm samples. This estimation bias is eliminated in firms listed on the Korea Exchange (KRX) by controlling for the correlated omitted variables problem. However, for KOSDAQ-listed firms, controlling for omitted variables did not effectively eliminate the estimation bias. This result is considered to arise from differences in the informativeness of stock prices between the KRX and KOSDAQ markets. In additional analysis, the study examined the effect of the Basu model's estimation bias on the conservatism measure of Khan and Watts (2009). For the KRX sample, it was confirmed that the process of calculating the Khan and Watts (2009) measure effectively controls for a substantial portion of the Basu model's estimation bias. However, for the KOSDAQ sample, the Khan and Watts (2009) measure was found to be significantly affected by the estimation bias.