Accessory fissures serve not only as natural barriers against infection but also help in localizing any focal pulmonary parenchymal diseases and in distinguishing pleural from parenchymal diseases. Knowledge of these fissures might be useful in differentiating unusual forms of atelectasis or consolidation occuring adjacent to the fissure. Left minor fissure (LMF) is a kind of unusual accessory fissures of the left lung, which separates adjacent segments of the upper lobe as clefts of various depths lined by two layers of visceral pleura. In this study, 4 cases of LMFs found in the left upper lobe during a routine dissection of 36 cadavers were observed. Of the 4 cases, 3 cases were true LMFs which located between the anterior segment of the upper lobe and superior segment of lingula, and 1 case was considered as left azygos fissure. Among the true LMFs, 2 LMFs coursed horizontally and 1 LMF coursed upward obliquely along the costal surface. The depth of LMFs was 0.5~1.2 cm and the length was 5~8 cm.