The present invention provides a process for preparing a highly active metallocene catalyst by which polyolefin having improved properties can be prepared with a small amount of cocatalyst. A process for preparing a metallocene catalyst of the invention comprises the steps of: modifying the surface of a zeolite or molecular sieve inorganic carrier possessing crystalline pores of 7 to 100 .ANG. size by the addition of an organic solvent and organic aluminum compound under an environment of inert gas and reacting at a constant temperature, and drying; and, impregnating a metallocene compound into the inorganic carrier by the addition of an organic solvent and said metallocene compound, whose diameter is smaller than the diameters of said pores of the inorganic carrier, to the inorganic carrier and reacting at a constant temperature, and drying. In accordance with the present invention, a highly active metallocene catalyst can be prepared in an economical and efficient manner.