A numerical study has been performed to investigate solidification process in a twin-belt caster that is one of the continuous casting process to produce thin slabs. Two parallel moving belts work as endless mold walls and the solidifying shell develops during passing through them. The numerical method is based on improved VOF (Volume of Fluid) method. Two-dimensional flow and temperature fields were obtained with computation parameters of belt speed, heat transfer coefficient between belt and metal, inlet nozzle width, and inlet temperature of metal. The solidification front agrees well with previously reported work.