Women of reproductive age with cancer face unique considerations in terms of fertility. The related decision-making process is complicated, and insufficient support can lead to decisional conflict. The aim of this qualitative systematic review was to identify and integrate qualitative evidence regarding the fertility decision-making process of women of reproductive age undergoing treatment for cancer. A qualitative systematic review was conducted following the Joanna Briggs Institute's methodology. Eight electronic databases were searched from inception to June 2023 for articles describing qualitative studies of the fertility decision-making process of women of reproductive age with cancer. Only original, full-text literature was examined, no limitation was placed on the publication language. Finally, 18 studies were included in a thematic analysis. We identified three analytical themes, namely "Perceived changes in fertility," "Influential participants in the decision-making process" and "Hard fertility decision-making processes of women," and nine descriptive themes that described the three analytical themes in detail. The results of qualitative synthesis emphasized that for women of reproductive age with cancer, fertility decision-making is a complex and dynamic process. These patients had experienced decisional conflict. Decision support from health care professionals was considered to be essential, and the use of patient decision aids in clinical settings was recommended. The synthesis results clarify women's fertility decision-making process, decision needs and the influencing factors, which offer evidence to guide the development of applicable patient decision aid tools to provide high-quality fertility services to women. TRIAL REGISTRATION: PROSPERO Registration Number: CRD42023434490.