The pulmonary lymphomas were thought to originate in specialized lymphoid tissue that is associated with bronchial mucosa(bronchus-associated lymphoid tissue(BALT)), and they were categorized as mucosa-associated lymphoid tissue(MALT) lymphoma. MALT lymphoma consists of a monoclonal population of cell, in contrast to reactive lymphoid proliferation, which consists of polyclonal cells. Lymphoma arising from MALT(=MALToma) represents a distinct clinicopathologic features. It is usually localized to their original site for a long time and shows much more favorable prognosis than lymphoma at other site. Some MALT lymphoma could arise simultaneously or successively in different organ or that cells from MALT lymphoma might circulate and give rise to another lymphoma by homing in the MALT of another organ, such as breast, salivary gland, stomach etc, and can be multifocally disseminated or recurred. We report a case of low-grade B-cell lymphoma of the mucosa-associated lymphoid tissue(MALT) of the lung, which was confirmed by open lung biopsy, immunohistochemistry and PCR assay.