This paper adopts Simunic’s (1980) audit-pricing framework and uses the propensity-score matching method to correct for sample selection bias related to observable differences between the Big4 and non-Big-4 groups to examine whether audit markets in case of listed companies remain competitive in Taiwan. The finding shows that Big 4 firms charge higher fees in both large and small client segments. In addition, the results of Rosenbaum bounds test suggest that the above empirical result is insensitive to the bias problems caused by unobservable factors. Overall, the result supports that the Big4 audit fee premiums may be due to audit-quality differentiation and audit market in the segment of listed companies in Taiwan is still competitive.