Background: We have already known that idiopathic granulomatous mastitis (IGM) is a rare benign chronic inflammatory disorder that can clinically mimic breast carcinoma, especially affects parous women of childbearing age, but there is little literature to report about pregnancy associated granulomatous mastitis (PAGM). The aim of our study is to report and describe the clinical signs, managements, clinical course, and clinical outcomes after treatment of PAGM in our hospital. Methods: We retrospectively analyzed 15 pregnant patients who were diagnosed as PAGM in our hospital collected from December 2018 to December 2020 by reviewing medical records and questionnaire survey, including the patients' characteristics, clinical presentations, microbiological workups, tissue pathology, treatment modalities, outcomes, and follow-up data. Results: The mean age of these patients at diagnosis was 30.5 (range 24-35) years. All patients had one birth before, and had at least two gravida times, 6 of them (40%) had three gravida times, and only one of them had four gravida times at diagnosis. The mean weeks of gestational age were 23.7 (range 4-37) weeks. Two patients' BMI were greater than 30, which were considered obese. The mean time to presentation since last delivery was 38.4 (range 19-78) months. All patients had a history of breastfeeding; the average breastfeeding time was 12.97 months. Just 2 of them were diagnosed with lactational mastitis before. One patient smoked before, 1 patient had oral contraceptive pills before, 4 patients had breast trauma recently, 5 patients had positive bacterial culture of pyogenic fluids, 3 patients had nipple retraction, 6 patients had abnormal humoral immunity, shown as elevated C3 or C4, and 2 patients had elevated serum prolactin. All patients presented as a breast mass with pain; two of them had erythema nodosum and oligoarthritis. Nearly all patients had unilateral lesion. The mean follow-up was 11 (range 1-24) months. Thirteen patients gave birth to a healthy baby, and all babies had a healthy growth and development. Almost all patients chose observation during pregnancy. Nine patients demonstrated complete remission, five of them underwent surgery after steroids and/or antibiotics, one patient had observation alone, two chose postpartum steroids alone, and the last one chose postpartum antibiotics alone. The average time to complete remission was 11.2 (range 7-18) months. Conclusions: In general, PAGM is a much rare disorder which has onset during pregnancy, and mainly happens in the second trimester and the third trimester. PAGM patients were all parous women and generally within 5 years of their last pregnancy, also with uncertain etiology and pathogenesis. Observational therapy during pregnancy for PAGM is reliable and feasible.