Immune cells - macrophages induced by E. coli K88 will lead to a pro-inflammatory response, which is important in host defense. Cathelicidin-WA (CWA) is an efficient antimicrobial peptide (AMP) and can exert immunomodulatory properties. Many studies have demonstrated that AMP can modulate cellular subsets but whether CWA can regulate macrophage polarization by transferring E. coli K88-induced M1 macrophage towards M2 one that of anti-inflammation remains unclear. In this study, E. coli K88 increased the expression of pro-inflammatory cytokines interleukin-6, interleukin-1β, tumor necrosis factor-α and chemokine CCL3 in RAW264.7 cells with a time-dependent manner, as well as the expression of reactive oxygen species (ROS) and inducible nitric oxide synthase (iNOS). On this basis, CWA significantly decreased the pro-inflammatory molecules but increased the anti-inflammatory mediators interleukin-4, interleukin-10 and other M2-related genes in E. coli K88-induced macrophages. Western blot analysis indicated that CWA suppressed the expression of TLR-4 and the phosphorylation of STAT1 and NF-κB which modulated M1 macrophage while induced the phosphorylation of STAT6 which activated M2 macrophage. Double staining of M1-specific CD86 and M2-specific CD206 also proved the hypothesis. These results suggested that CWA might dampen the inflammation by modulating M1 phenotype to M2 phenotype in E. coli K88-induced macrophages.