Expansion during fermentation on Medium-Chain Triacylglycerols (MCT) oil-based doughs compared to butter fat-based doughs were studied, and the mechanism of fermentation accelerator of MCT oilbased in dough was also investigated. The results obtained as follows; the concentration of MCT oil-based accelerator on the fermentation of dough was confirmed maximum at 6.0%. The rate of expansion became the maximum a 60% of gluten contents at the dough with MCT oil-based. Mechanism of expansion of fermentation on MCT oil-based doughs was discussed. Gluten is formed of gliadin and glutenin. Gluten was denatured by MCT oil-based, which gluten molecule grows large. Fermentation is promoted by this phenomenon. This fact can provide new information to the bread-making industry.