In order to study the effect of glycosylation on its biological activities and to develop tumor necrosis factor alpha (TNFalpha) with less deleterious effects, N-acetylneuraminic acid (NeuAc) with a C9 spacer was chemically coupled to human recombinant TNFalpha. NeuAc-coupled TNFalpha (NeuAc-TNFalpha) exhibited reduced activities in vitro by about threefold compared to native TNFalpha. In this study, we examined a variety of TNFalpha activities in vivo. NeuAc-TNFalpha reduced activities in the up-regulation of serum levels of IL-6 and NOx, but comparable activity as native TNFalpha in the down-regulation of the serum level of glucose. However, NeuAc-TNFalpha was more potent than TNFalpha in the up-regulation of the serum level of serum amyloid A (SAA). NeuAc-TNFalpha was less toxic to mice. In addition, NeuAc-TNFalpha exhibited an augmented anti-tumor activity against Meth-A fibrosarcoma without hemorrhagic necrosis. These results indicate that coupling with NeuAc enabled us to develop neoglycoTNFalpha with selective activities in vivo, including enhanced anti-tumor activity but reduced toxicity.