Abstract: Lithophysae, which commonly occur in rhyolite and rhyolitic welded pyroclastic rocks, preserve evidence of the cooling, consolidation, and emplacement processes that followed eruption. This study takes the lithophysae within the welded tuff and rhyolite of the Fangshan Caldera in Wenling, Zhejiang Province as the research object, conducting field investigations, petrography, geochemistry, and X-ray CT scanning, to reveal the distributions, petrographic characteristics, and volcanological significance of these two types of lithophysae. The lithophysae-rich layers can be observed at the top of the profile of the welded tuff. The lithophysae within the welded tuff display spherical or lenticular shapes, with diameters ranging from 1 to 30 cm, and contain circular and sickle-shaped cavities that are partially filled. The walls of these lithophysae are composed of radiating fibers. The lithophysae within the rhyolite, which are widely distributed, display a spherical shape with diameters ranging from 0.5 to 20 cm, and contain circular to irregular cavities that are partially or completely filled with quartz (agate). The walls of these lithophysae display radiating fibrous textures, exhibiting concentric growth rings and oxidation rims. The layered distribution of the lithophysae in the profile of the welded tuff suggests that the growth process of the lithophysae was constrained by volatile components, and reflects that the welded tuff from Fangshan Caldera was formed by the progressive aggradation of three flow units. The concentric growth rings and oxidized rims of the lithophysae within the rhyolite indicate that the nucleation and growth of the lithophysae occurred at or above the glass transition temperature. According to estimates based on published experimental petrological data, it took approximately 87 to 521 days for the walls of the lithophysae to grow to a radius of 2 cm. This suggests that the lava flow of the Fangshan Caldera underwent a relatively slow cooling process and that the rhyolite may represent a proximal effusive facies associated with an extrusive dome in a volcanic conduit. This study provides new evidence for research on Cretaceous volcanism and volcanic geological surveys in the coastal area of southeastern China.