In this paper, the writers studied on the morphological characters of the zircon crystals from the pyroclastic volcanic rocks in Japan and obtained the following results; i) In the pyroclastic volcanic rocks, the zircons are contained in much smaller amount than in the granitic rocks and the grain sizes are mostly very minute ranging from 0.02×0.01mm. to 0.50×0.25mm., and 0.10×0.05mm. in common. ii) The crystal tracht is characterized with Yamamoto's ‘c’-type same as that from granitic rocks and rhyolites. iii) By the I-R-U trigonal diagram of the crystal forms, it was ascertained that the rounded crystals (R) and the broken ones are remarkably contained. The above-mentioned facts lead to us that the original pyroclastic volcanic rock magma might have been contaminated or assimilated by a large amount of sedimentary rocks.