A rotary kiln type reactor is developed to control the triboelectric charge of crosslinked polystyrene microspheres by low temperature plasma treatment. Four kinds of plasma gass (Ar, O-2, CO2 and NH3) were used as plasma gases. From surface analysis and measurements of the triboelectric charge of plasma-treated microspheres, the following results are obtained. (1) Plasma treatment with various gases makes it possible to incorporate various functional group such as amino, carbonyl and peroxy groups on the surface of the microspheres. (2) Sign and triboelectric charge of the polymer microspheres are able to be charged by changing charge gas and treatment time, respectively.