The image-on-image (IOI) color process, in which color images are superimposed on a single photoreceptor drum and then transferred to the paper at once, possesses capabilities for realizing a high speed, high quality, and compact color printer. However, in the IOI processes using dry toners, there are unavoidable problems that make it difficult to obtain high quality color images. The authors found that, using liquid toners, these issues are completely resolved and an excellent color process is realized. Development characteristics and color image qualities are compared between IOI processes using dry and liquid toners. The results of theoretical analyses agree with these experimental data.