Since the use of rubber materials has been increasingly developed in the printing industry, it would be most interesting from practical point of view to investigate the effect of cleaning solvent and printing ink vehicle upon offset rubber blanket. So the authors conducted several experiments. A commercial offset blanket was cut and stripped into chips of 1cm×4.5cm and used as samples. As a preriminary examination, the samples were immersed in 4 types of mineral oils?namely motor gasoline (4), mineral spirit (50), kerosene (9) and light oil (14) respectively at 25°C, and increases in weight were measured. The results were presented in Fig. 1 as swelling curves. This weighing method is, however, somewhat tedious, especially in case high volatile solvent is used. While it was ascertained by Y. Tanaka, S. Kambara and 5. Noto (5. S. C. I., Japan, 1905, 38,364 B) that the swelling degree of vulcanized rubber could be expressed in terms of the elongation. So the authors observed, using the apparatus showed in Fig. 2, elongations of immersed samples in the mineral oils, benzene, toluene, xylene, carbon tetrachloride, ethylene dichloride, acetone and alcohol, and then shrinkages during the course of their deswelling in open air. The sesults were presented in Fig. : 3, 4, 5. It was experimented further on various concentrations of lithographic varnish-motor gasoline solutions to investigate the effect of printing ink vehicle dissolved in cleaning solvents at the time of washing. The results were presented in Fig. 6, 7, 8, 9, 10. The most important property of rubber washing solvents may be volatility, for a high volatile solvent, though its swelling power may be somewhat strong, evaporates almost at once, so that no permanent damage is done, whereas a less volatile solvent swells rubber for a long time and continues its softning effect. It was concluded that, among the 4 types of mineral oils, motor gasoline is most suitable for use as a rubber washing solve lt because of its high volatility and comparatively low final swelling degree. On the other hand, ethylene dichloride may be recommended as the washing agent among the other synthetic solvents. When the washing is carried out, however, dissolved ink vehicle in cleaning solvent also penetrates into rubber and remains in it even after drying, as is illustrated in Fig. 10. It is well known that, although the swelling action of printing ink vehicle is generally far less than that of cleaning solvents, the influence of swelling itself nevertheless dreadful. In this experiments, however, it was proved that the most poisonous ingredients in printing ink vehicle were mineral oil and fatty acid, as is illustrated in Fig. 11, 12.