The study aimed to evaluate the effects of an expressive writing intervention on quality of life (QoL) among mainland Chinese breast cancer patients. A total of 118 Chinese breast cancer patients were randomly assigned to one of four groups: a cancer-facts writing condition (CTL group), an emotional disclosure writing condition (EMO group), a self-regulation writing condition (SR group), or a neutral control condition with no writing tasks (CON group). QoL was assessed by FACT-B at baseline, 3-, and 6-month follow-ups. A repeated measure analysis of variance revealed significant effects of time (F = 13.9, P < 0.001, η2 = 0.20) and the time × group interaction (F = 3.5, P < 0.01, η2 = 0.08) on QoL. Residualized change models showed that the CTL, EMO and SR groups reported higher levels of QoL than the CON group at the 6-month follow-up. The EMO group had a higher level of QoL than the SR group. The CTL group had higher level of physical well-being compared to the SR group. Mainland Chinese breast cancer patients shortly after diagnosis benefit from expressive writing. They benefited more from cancer-facts and emotional disclosure compared to self-regulation. The study indicated that the impact of expressive writing may differ due to stage of cancer survivorship, social, and cultural context.