We observed in situ the free-growth forms and measured the growth velocity of tetra-n-butyl ammonium bromide (TBAB) semi-clathrate hydrate single crystals. The free-growth forms changed with supercooling, however the crystals were columnar at all supercoolings measured, up to 2.4 K. The side surfaces had a critical supercoolings of about 1.4 K, below which growth was not measured. At the bottom surface, the growth roughening was observed at the supercooling 0.9 K. These results show that the growth of TBAB hydrate is extremely affected by interfacial kinetics. (C) 2004 Elsevier B.V. All rights reserved.