We examine whether Big Four auditors influence the financial reporting quality of Chinese firms audited by non-Big Four auditors through learning by interlocked audit committee (AC) members. We document that non-Big Four clients exhibit significantly higher reporting quality when their AC members concurrently serve on the ACs of Big Four audited firms. This spillover effect is more pronounced when AC members have stronger incentives to learn or when alternative learning channels are limited. The observed AC learning appears to reflect exposure to recent developments in accounting and auditing standards, as well as enhanced understanding of business and risk environments. In contrast, we find no comparable effect associated with interlocks involving China's top domestic audit firms. These findings highlight the positive externality of Big Four auditors in enhancing financial reporting quality in China, facilitated by on-the-job learning among AC members who serve clients across both Big Four and non-Big Four firms.