Abstract: The injection of large argon flow into ladle shroud was adopted in continuous casting production in order to produce fine argon bubbles in tundish. In this study, the bubbles were captured by dipping a cold steel sheet into molten steel. The captured bubbles at the surface of hot-dipped steel sheet, with a size of 1.0-3.0 mm, characterized the argon bubbles at steel/slag interface and slag phase in the upper part of tundish instead of those inside molten steel in tundish. The latter could be characterized by the captured bubbles in the interior of hot-dipped steel sheet, and their morphology, size, and number were analyzed by scanning electron microscopy and confocal microscopy. The bubbles inside molten steel in tundish generally had a spherical shape and occasionally adhered to each other. The size of bubbles was in the range of 100-1000 μm, with an average of about 500 μm. The bubbles were more dispersive at the exit of ladle shroud and its lower position, with a density of 15.2 per square centimeter. Moreover, it was observed that, for part of bubbles, a bubble could adhere to an inclusion, even multiple inclusions. The adhesion of bubbles to Al2O3 inclusions was higher than that to CaO(-MgO)-Al2O3-SiO2 complex inclusions.