Our findings reveal that 1,25(OH)2D3 promotes M2 polarization (CD163+/Arg-1+) while suppressing M1 phenotype (iNOS+) in in vitro co-cultures, in vivo co-xenograft and DEN/CCl4-induced HCC mouse models, resulting in increased M2: M1 ratio. The gene discussed is ARG1; the disease is hepatocellular carcinoma.