Antepartum mastitis is a rare condition, whereas postpartum or lactation mastitis is a common problem. This report introduces a case of complicated bilateral antepartum mastitis, which was treated successfully by drain insertion and antibiotic therapy. The patient was a 23-year-old woman in the 23rd week of her first pregnancy. Her chief complaint was progressive swelling, redness and radicular pain in both breasts, which had been started gradually from the 18th week of pregnancy. The patient was admitted to hospital, and received oral and intravenous antibiotics empirically, which was not effective. The patient was treated by drainage and oral antibiotic therapy. Based on the approaches employed and the outcomes achieved it is suggested that early surgical insertion in the presence of fluid collection in antepartum mastitis will shorten hospitalization and course of intravenous antibiotic therapy.