This study describes foreign particle behavior at the growth interface of tetrahydrofuran (THF) clathrate hydrates in a THF-water solution containing a small amount of silica beads. The hydrate was grown at a constant growth rate using a directional growth apparatus. Bead behavior at the growth interface was observed in situ using a microscope. The results showed that the growth interface pushed the beads at lower growth rates but encapsulated them into the crystal region at higher growth rates. A critical growth rate V(c) was shown to exist below which a bead is pushed by the growth interface. V(c) was almost inversely proportional to the bead diameter. This tendency corresponds to the theoretical and experimental studies on particle behavior during ice growth. (C) 2010 Elsevier B.V. All rights reserved.