The rapidly growing nontuberculous mycobacteria, Mycobacterium fortuitum are of increasing clinical importance. The ubiquitous M. fortuitum has been isolated from water, soil and dust. M.fortuitum usually causes skin or soft-tissue infections through direct inoculation occurring in surgery or penetrating trauma but may infect a wide variety of tissues including the lungs, lymph nodes, bones, joints and meninges. We believe this is the first report of breast abscess due to M. fortuitum, which presented in an immunocompetent woman in Korea after nipple piercing. A 26-year-old female presented with a 5-month history of a tender Rt. breast lump that was gradually increasing in size after nipple piercing. Ultrasound examination showed a poorly marginated lesion with areas of cavitation. Open biopsy with debridement found solid and necrotic tissue without purulence. Histologic examination confirmed granulomatous inflammation. Culture grew Mycobacterium fortuitum. The Rt breast abscess were improved by antibiotic therapy with doxycycline and moxifloxacin for 6 month. When breast abscess is recurrent and bacterial cultures are sterile, mycobacterial infection should be considered, particularly when there is a history of previous nipple piercing procedures.