The influence of toner shape on the toner performance was investigated. Toner particles were thermally or mechanically modified to make variations in shape from irregular to quasispherical shape. In addition to the typical developing characteristics such as transfer efficiency, the developing characteristics were investigated by observing the degree of toner contamination on the developing roller with an electron microscope and measuring the charge of the toner particles on the developing roller on continued development. It was found that the surface of the developing roller was gradually contaminated to form an additional thin film made of toner materials after a long run developing process. This contamination played a major role in the decrease of the toner charge, especially in the late part of the cartridge life. The degree of contamination was found to be dependent critically on the toner shape and the structure of the toner surface. Both thermal and mechanical modifications worked to reduce the contamination, thus improving the lifetime of toner performance.