An air cavity is formed behind a spherical particle plunging into a liquid bath. The residual bubble attached to the sphere has an important effect on the performance of CaO particle used for desulfurization of melted iron. Based on the water model with the same kinematic viscosity as the melted iron, the behavior of air cavity was observed for the spheres coated by two kinds of water repellent preparations. In this report, the volume of residual bubble was theoretically estimated for the quasi-static immersion of sphere as a reference condition. First the critical depth at which the axi-symmetric meniscus breaks is obtained by using Laplace equation. Then the bubble volume was obtained from a simple energy minimum principle in which we considered the effect of the interfacial energy including the wetting behavior and the liquid potential energy. The calculated volumes can approximate fairly well the measured results for two kinds of contact angles of 115° and 162°.