To provide a stable preparation process of a uniform resin mixture with little dispersion which gives a uniform resin composition or resin molded product with little dispersion by melt kneading this mixture.

In a preparation process of a resin mixture comprising two or more particulate resins and one or more powdery resin, two or more particulate resins are pre-mixed in a rotary mixer to form a pre-mixture which is subsequently mixed with one or more powdery resin. Here, two or more particulate resins are pre-mixed in the presence of 0.01 to 10 wt.% antistatic agent against the total weight of the pre-mixture. Furthermore, the pre-mixing of two or more particulate resins is conducted by rotating the rotary mixer 250 to 1,000 times at a rotation speed of 15 to 45 rotation/min.