This study links the gender diversity of the top management team (TMT) to corporate social responsibility (CSR) and examines the moderating role of the marketization level in their relationship. According to the token theory, females are “tokens” and have difficulty playing their roles when they are rare in groups, where their presence is used for providing legitimacy. Meanwhile, CSR is implemented to gain legitimacy. Therefore, we predicted that there was a negative relationship between female top managers and CSR, and that the marketization level positively moderated their relationship. The hypotheses were supported by the data from 17,032 manager-year observations of listed companies in China. The results indicated that the female top managers’ presence and CSR performance had the same function of gaining legitimacy. With limited resources, firms added females at the expense of decreasing investment in CSR when under the external pressure of increasing female top managers. Furthermore, this negative relationship was stronger in firms with a less-developed institutional environment because firms with weak institutions have strong incentives to find alternatives to fill the institutional void, which helps to gain access to resources and reduce transaction costs.