The process of ink droplet formation in ink jet printing was observed by a micro image monitoring system synchronized with a printer head driver. Two types of jet ink, dye solution type and pigment suspension type were investigated.The jet forming process is associated with viscoelastic properties of jet ink. Therefore, rheological properties of jet inks have been discussed. The printed dot pattern was observed using a specially designed dynamic simulation system. The effect of scanning velocity of printer head on dot pattern was investigated in connection with satellite formation. In order to evaluate the print quality on a paper, we used three parameters; 1. fractal dimension for dot outline, 2. optical density, 3. ratio of dot and droplet diameter.The useful information for printability of ink jet printing was obtained.