Although polyphosphate [poly(P)], a linear polymer of orthophosphates, is found in various tissues, its function remains largely unknown. We previously reported that the treatment with poly(P) reduced the expression of inducible nitric oxide synthase (iNOS), an inflammatory mediator, in macrophages activated by bacterial lipopolysaccharide (LPS). In this study, we show that LPS-induced expression of chemokine (CXC motif) ligand (CXCL) 10 is also decreased by poly(P). Poly(P) consistently inhibited the phosphorylation of signal transducer and activator of transcription (STAT) 1, a transcription factor for CXCL10 and iNOS, from 2 to 24 h after LPS treatment. The activation of Janus kinase (JAK) 1 and tyrosine kinase (TYK) 2, which phosphorylate STAT1, was suppressed by poly(P) at 2 h but not 12 h. At 12 h, poly(P) enhanced the activation of Src homology-2 domain containing protein tyrosine phosphatase (SHP) 2, which dephosphorylates STAT1. These results suggest that poly(P) suppresses LPS-induced STAT1 activation through at least two different mechanisms, the inhibition of JAK1/TYK2 and the activation of SHP2, resulting in decreased production of CXCL10 and iNOS. This may affect inflammation and host defense against infection.