Several studies suggest that the inflammation plays a role in the pathogenesis of some glucose disorders in adults. Exposure of pancreatic β-cells to cytokines, such as interleukin-1β (IL-1β), is thought to contribute to β-cell apoptosis. One important event triggered by IL-1β is induction of nitric oxide synthase (iNOS), an enzyme that catalyzes intracellular generation of the cytotoxic free radical NO. Recent work have suggested that formononetin, as an <em>O</em>-methylated isoflavone found in a number of plants and herbs like <em>Astragalus membranaceus</em>, inhibited some pro-inflammatory cytokine production in macrophages. However, the roles of formononetin in pancreatic beta cells have not been fully established. The aim of the present study was to assess possible <em>in vitro</em> effects of formononetin on cell apoptosis induced by IL-1β in the rat insulinoma cell line, INS-1. Our results demonstrate that formononetin significantly prevents IL-1β-increased INS-1 cell death and blocks cytokine-induced apoptotic signaling (the reduction of Bax/Bcl-2 ratio and caspase-3 activity). Formononetin also inhibited the activation of nuclear factor-kappaB (NF-κB), which is a significant transcription factor for iNOS, so as to decease nitric oxide (NO) formation in a dose dependent manner <em>in vitro</em>. Our observations indicated that formononetin could protect against pancreatic β-cell apoptosis caused by IL-1β and therefore could be used in the future as a new drug improving diabetes mellitus.