The effects of magnesite diameter on the magnesite reforming rate were experimentally investigated. When magnesite alone was heated, the reforming rate decreased with increasing magnesite diameter. For mixtures of magnesite with addition of the magnesium nitrate hexahydrate, the magnesite reforming rate constants were similar to those without magnesite nitrate hexahydrate, when the magnesite diameters were greater than 10(-3) m, and greater than that without magnesium nitrate hexahydrate when the magnesite diameters were smaller than 10(-3) m. In the mixtures with magnesium nitrate hexahydrate, the magnesite reforming rate constant is inversely proportional to the square of the magnesite diameter.