In inflammatory bowel diseases, interleukin-1β production is accelerated. Butyrate, a short chain fatty acid, plays an important role in inflammatory bowel diseases. We investigated the effect of butyrate on interleukin-1β production in macrophage and elucidated its underlying mechanism. We stimulated THP-1 cells, a human premonocytic cell line, by lipopolysaccharide alone and by butyrate with lipopolysaccharide. Butyrate with lipopolysaccharide increased interleukin-1β production more than lipopolysaccharide alone. Butyrate with lipopolysaccharide increased caspase-1 activity more than lipopolysaccharide alone. As for the phosphorylation pathway, PD98059 (ERK1/2 inhibitor), SB203580 (p38 MAPK inhibitor), SP600125 (JNK1/2 inhibitor) decreased caspase-1 activity and interleukin-1β production to approximately 50% of the controls. Pertussis toxin (G protein-coupled signal transduction pathway inhibitor) also reduced interleukin-1β production to approximately 50%. Butyrate with lipopolysaccharide increased reactive oxygen species levels more than lipopolysaccharide alone. The addition of N-acetyl L-cysteine reduced reactive oxygen species levels to a level similar to that of lipopolysaccharide alone. Butyrate with lipopolysaccharide increased nitric oxide production more than lipopolysaccharide alone, and the addition of N-acetyl L-cysteine reduced the elevated amount of nitric oxide. In conclusions, butyrate enhances interleukin-1β production by activating caspase-1, via reactive oxygen species, the phosphorylation of MAPK, and G protein mediated pathways in lipopolysaccharide stimulated THP-1 cells.