Abstract: Objective：To investigate the expression of arginase-2 (Arg-2) in lung adenocarcinoma and its clinicopathological significance. Methods：Reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting were respectively used to detect the expressions of Arg-2 mRNA and protein in 7 cases of lung adenocarcinoma and paracancerous lung tissues, and 1 case of normal lung tissues. The immunohistochemical method was used to detect the expression and location of the Arg-2 protein in the paraffin specimens of 108 patients with lung adenocarcinoma. The correlation of Arg-2 expression with the clinicopathological indexes of lung adenocarcinoma and the prognosis of patients were analyzed. Results：Arg-2 mRNA and protein expression levels in lung adenocarcinoma tissues were significantly higher than those in adjacent and normal lung tissues. Immunohistochemistry showed that the positive signal of Arg-2 protein was located in the cytoplasm. In 108 cases of lung adenocarcinoma, 74 cases had low expression of the Arg2 protein, other 34 cases had high expression. The positive expression rate of Arg2 in lung adenocarcinoma was higher than that in adjacent tissues (P<0.000 1). The high expression of Arg-2 was positively correlated with the differentiation degree of lung adenocarcinoma (P=0.000 6), lymph node metastasis (P=0.002 8), TNM stage (P=0.021 5), and Ki-67 cell proliferation index (P<0.000 1). The overall survival rate of Arg-2 high expression group was significantly lower than that of Arg-2 low expression group (χ2=6.762, P=0.009). Multivariate Cox proportional hazards model analysis showed that Arg-2 high expression was not an independent prognostic factor for lung adenocarcinoma(P=0.051). Conclusions：Arg-2 is associated with the proliferation, differentiation, lymph node metastasis and TNM stage of lung adenocarcinoma. The high expression of Arg-2 indicates that the prognosis of lung adenocarcinoma is poor, but it is not an independent prognostic factor.