Outgassing tests for various types of isotropic graphites have been carried out and the effect of the rinse material for ultrasonic cleaning has also been investigated.The results obtained are summarized as follows:o(1)Total outgassing yields for as-received graphites tend to increase with increasing apparent density;(2)for very-dense graphites, the total outgassing yield from the near surface region is much more significant than that from the bulk;(3)rinsing as-received graphites with either acetone or alcohol reduces outgassing, whereas little effect is seen with water;(4)outgassing from the graphite, once outgassed above 1500 K, is quite small;(5)after once being outgassed, the amount of gas uptake upon exposure to air or water vapor is not serious.