ObjectiveTo investigate the expressions of microRNA-155 (miR-155) in different phenotypes of activated macrophages. MethodsThe THP-1 cells underwent polarized activation into M1, M2 or tumor-associated macrophages (TAMs), and the phenotypes were confirmed by flow cytometry. The miR-155 expression was determined by qRt-PCR in M1 macrophages, M2 macrophages and TAMs. ResultsThe miR-155 expression significantly decreased in the M2 macrophages (1.83±0.337, P=0.000), TAMs (1.60±0.233, P=0.000) compared with the M1 (6.580±0.637). The phenotype of TAMs was similar to M2. There was no statistically significant difference between TAMs and M2 macrophages in the expression of miR-155 (P=0.546). ConclusionDifferent expressions of miR-155 in macrophages M1-type and M2-type may be associated with the differentiation or their cellular functions. The phenotypic characteristics TAMs may transform to macrophages to M2-type. And they may have the same functions.