The three-dimensional linear stability of the steady mixed-convective flow in a (moderately) wide gap annulus between two concentric horizontal cylinders with a heated rotating inner cylinder is studied numerically. The critical stability curves in the parameter plane of (Re?, Gr) are determined. It is found that the effect of heating of inner cylinder postpones the formation of Taylor vortices when the rotation effect dominates the buoyancy effect. When the effect of buoyancy predominates over the effect of centrifugal force, the rotation of inner cylinder also stabilises the mio-dimensional basic flow. When both rotation and buoyancy effects are important, the basic flow becomes unstable with respect to oscillatory disturbances. The results are in qualitative agreement with those of the three-dimensional numerical computations.