This is a review on toxicity reduction of proton therapy for breast cancer including cardiac toxicity, secondary cancer and radiation pneumonitis. It has been verified that PT can decrease the dosage of the heart and left anterior descending artery in individuals diagnosed with left breast cancer, data support the potential benefits of PT compared to conventional radiotherapy for the heart. PT reduces risks of secondary lung cancer and contralateral breast cancer compared to IMRT and 3DCRT. PT reduces radiation-induced pneumonitis, especially for patients received regional nodal irradiation. Recent studies showed skin toxicity with PT predominantly grade 1–2, with minimal or no toxicity exceeding grade 2. Patients experienced high levels of satisfaction with the long-term follow-up in terms of cosmetic outcomes, without any impact on their survival. However, in patients receiving IMPT treatment, reconstruction complications are still a problem of clinical significance.