During spark plasma sintering of transparent ceramics, the effects of heating rate, pressure and loading schedule on the grain size are examined. When alumina is densified at low temperatures, high heating rates accelerate grain growth, though the total heating time is reduced. The accelerated grain growth may result from the generation of defects during densification. The defects may enhance the grain-boundary mobility and accelerate the grain growth rate, that is the dynamic grain growth. It is considered, therefore, that the high deformation rate at high heating rates accelerates grain growth. The accelerated grain growth also appears for high-pressure sintering. The grain size after sintering increases with the applied pressure. In addition, the loading schedule during heating also affects the deformation and the grain growth. In this study, the unusual grain growth during sintering of transparent ceramics is explained by using the concept of dynamic grain growth.