To obtain sufficient specimens for the histological diagnosis is necessary for the treatment of malignant lymphoma. We carried out open biopsy for malignant lymphoma of the anterior mediastinum in 4 patients from 2011. They were consisted of 1 male and 3 females, aged in average 27-year old. Core needle biopsy proceeding open biopsy failed to diagnose the tumors in 3 patients. The quality of biopsy specimens were certified by frozen section immediately. Sufficient specimens were obtained from all patients.