Provided is a method of evaluating the kneading efficiency of a sealed rubber kneading machine whereby the degree of kneading efficiency of the kneading machine can be easily and accurately grasped. When a kneading material containing raw material rubber and carbon black R is kneaded with a sealed rubber kneading machine (1), a calculation device (11) calculates an evaluation index E on the basis of the total shear amount J, found by integrating over the kneading time T the shear velocity gama applied to the kneading material R by a rotor (8) driven by a rotor drive unit (10) of the kneading machine (1), and the unit work UW, found by dividing the total power consumption UW (i.e. the instantaneous power of the rotor drive unit (10) integrated over kneading time) by the mass M of the kneading material. The degree of kneading efficiency of the kneading machine (1) is evaluated depending on the magnitude of the evaluation index E which calculated as the unit work / total shear amount.