We separated volcanic glasses from the Eocene-Oligocene transition interval at Integrated Ocean Drilling Program Site U1333, drilled during Expedition 320. Among 23 sediment samples we found five samples that contain volcanic glasses: one from Eocene radiolarian ooze and the others from Oligocene calcareous ooze. Glass shards were separated by handpicking from coarse sediment fractions (>75 mu m in size), which are composed mainly of microfossil fragments (radiolarians and foraminifers). Volcanic glasses from these five samples are dominated by clear silicic glass shards 80-300 mu m in size, but we cannot find other minerals such as quartz and feldspars or shards of brownish glass of dacitic composition. The glass shards are classified into three types based on their morphology: (1) flat to weakly concave (concoidal) shards without junctions (plate-type), (2) shards forming elongated fibrous to tubular vesicle walls (tube-type), and (3) fragments of globular bubbles (balloon-type). Electron microprobe analyses of 181 glass shards from interval 320-U1333C-14H-6W, 92-94 cm, revealed that the glass shards have uniform rhyolitic compositions relatively rich in alkaline elements (Na and K) but depleted in Fe, Mg, and Ca. These results suggest that the origin of these glass shards was explosive silicic volcanos with either a single source or a mixture of multiple sources with similar compositions. The five samples that contain volcanic glasses suggest episodic explosive volcanic eruptions at this time. Given the rhyolitic compositions and proximity of Site U1333 to Central America, we regard Central American arc volcanism as the most likely source of the glass shards found at Site U1333.