Objective: To evaluate the safety, cosmesis, and clinical outcome of intraoperative electron radiation therapy (IOERT) delivered prior to lumpectomy for early-stage breast cancer.Methods: From December 2008 to March 2012, 75 breast cancer patients (ages 34-66 years) were treated with IOERT during breast conservative surgery.IOERT was delivered using a mobile linear accelerator.Suitable energy and applicator size were chosen to ensure coverage of the tumor with anterior and posterior margins of 1 cm and lateral margins of 2 cm.Patients with sentinel node metastases or younger than 40 years received 8 Gy as boost followed by post-operative external beam radiation therapy of 50 Gy/25F;the others had 15 Gy, prescribed to the 90% isodose depth.Adjuvant treatment consisted of chemotherapy (55 patients), hormonal therapy (59 patients), or combined chemotherapy and hormonal therapy (41 patients).The safety, cosmesis, and short-term outcome were evaluated.Results: Median follow-up was 54 months (range: 30-66 months).Two (2.7%) patients developed post-surgical hematoma.Six (8.0%)patients developed mild breast fibrosis.Eight (10.7%) patients suffered from local pain.One (1.2%) patient experienced a post-operative infection.Sixteen (21.3%) patients developed Grade 1 pulmonary fibrosis.Forty-three (57.3%) patients had an excellent cosmetic result and 23 (30.7%) had a good cosmetic result.Three patients had an ipsilateral breast recurrence, with an actual 3-year local recurrence rate of 4.0%.One patient had an ipsilateral axillary recurrence, resulting in a 3-year regional recurrence rate of 1.3%.No distant metastases or deaths were observed.The 3-year disease free survival was 94.6%.Conclusions: Intraoperative electron radiation therapy delivered prior to lumpectomy is safe and feasible for selected patients with early-stage breast cancer.Early side effects,cosmesis and short-term efficacy are acceptable, but a longer follow-up is needed for evaluation of late side effects and long-term outcome.