Upregulation of pro-inflammatory mediators contributes to β-cell destruction and enhanced infiltration of immune cells into pancreatic islets during development of type 1 diabetes mellitus. In this study, we examined the regulatory effects and the mechanisms of action of celastrol against cytotoxicity and pro-inflammatory immune responses in the RINm5F rat pancreatic β-cell line stimulated with a combination of interleukin-1 beta, tumor necrosis factor-alpha, and interferon-γ. Celastrol significantly restored cytokine-induced cell death and significantly inhibited cytokine-induced nitric oxide production. In addition, the protective effect of celastrol was correlated with a reduction in pro-inflammatory mediators, such as inducible nitric oxide synthase, cyclooxygenase-2, and CC chemokine ligand 2. Furthermore, celastrol significantly suppressed cytokine- induced signaling cascades leading to nuclear factor kappa B (NF-κB) activation, including IκB-kinase (IKK) activation, IκB degradation, p65 phosphorylation, and p65 DNA binding activity. These results suggest that celastrol may exert its cytoprotective activity by suppressing cytokine-induced expression of pro-inflammatory mediators by inhibiting activation of NF-κB in RINm5F cells.