Objective This study examined the feasibility and acceptability of written exposure therapy (WET) in reducing symptoms of posttraumatic stress disorder (PTSD) in Iranian women with breast cancer. Secondary aims included examining the influence of WET on quality of life (QoL), overgeneral memory and illness perceptions. Method Forty‐six females with breast cancer and clinical symptoms of PTSD referred to the Razi Hospital in Rasht, Iran were randomly assigned to either WET (n = 23) or control (n = 23) groups. WET is a 5‐session low‐intensity exposure‐based intervention for treating PTSD. The control group had no additional contact. Measures assessing PTSD, illness perceptions, overgeneral memory, and QoL were administered at baseline, post‐intervention and 3‐month follow‐up. Results Acceptability of WET was high; all participants completed all WET sessions. At post‐intervention, 95.65% of the WET group met criteria for reliable change and 100% met criteria for minimal clinically important difference (MCID) and clinically significant change in PTSD symptom improvement. At follow‐up, all WET participants met criteria for reliable change, MCID and clinically significant change in PTSD symptom improvement. No participants in the control group met reliable change, MCID or clinically significant change. The WET group had improved QoL and memory specificity and decreased threatening illness perceptions at post‐intervention and follow‐up when compared to controls. Conclusion WET may be a useful intervention for use with breast cancer patients with PTSD symptoms and may be an important adjunct to medical and pharmacological treatments, particularly in low‐ and middle‐income countries. This study indicates further research in this area is warranted.