In high speed machining, thermal stability of spindle has a great influence on the machining accuracy and the machining efficiency. Thermal instability of spindle is caused by the thermal deformation of spindle. Thermal deformation of spindle may be reduced by changing the material of spindle. Carbon fiber reinforced plastics (CFRP) has the advantage of low coefficient of thermal expansion. In this paper, thermal deformation and dynamic characteristics were compared for shafts made of steel and CFRP, using finite element analysis and measurement tests.