Disclosed is a method for producing a modified conjugated diene polymer comprising a step for obtaining a modified conjugated diene polymer by reacting a conjugated diene polymer, which is obtained by bonding an alkoxysilyl group and an optionally protected primary amino group to a polymer containing at least a conjugated diene unit and has a weight average molecular weight of 150,000-2,000,000, with a metal halide. This method enables to desirably obtain a conjugated diene polymer having high Mooney viscosity, excellent shape stability and good workability.