To provide tantalum carbide powder and solid solution of tantalum carbide-niobium as raw material for composite material, each of which is composed of fine and uniform particles uniformly dispersed, also stoichiometrically sufficiently bonded with carbon and has a low oxygen content, and to provide their production methods.

Each of the tantalum carbide powder and tantalum carbide-niobium composite powder has a primary particle average diameter of 0.10 to 0.40 m measured by a specific surface area method (BET method), a secondary particle average diameter of 0.40 to 1.0 m measured by an FSSS method, and also has (the primary particle average diameter/secondary particle average diameter) within the range of 0.21 to 0.40.