China Securities Investor Services Center (ISC), acting as a regulatory minority shareholder, safeguards the legitimate rights and interests of minority investors through exercising their rights. Taking Ashare listed companies from 2016 to 2021 as research samples, the paper investigates the impact and mechanism of ISCs exercise of rights on internal control quality of enterprises. The study found that ISC can improve internal control quality. Mechanism testing shows that ISC improves internal control quality through two paths: information effect and governance effect. Further analysis shows that when ISC exercises its rights in the form of rights protection litigation, online exercise and sending shareholders suggestion letters, the internal control quality will be significantly improved. When the exercise content involves control environment inquiry and information and communication inquiry, internal control quality will be significantly improved. The exercise effect is more significant in companies with poor information transparency and low shareholding ratio of pressure resistant institutional investors. The research conclusion has important practical significance for further optimizing the exercise effect of the services center.