Experiments on thermocapillary convection of high-temperature Bi12SiO20 melts have been carried out. Thermocapillary convection has been identified to dominate the fluid flow in a layer of 70 mum thickness melt with Pr = 26 in the loop-like zone used in our experiments. The transition of the melt from steady spatial to oscillatory behavior under temperature difference of 120, 60 and 10K were considered. The oscillation of thermocapillary convection is characterized by the oscillatory main trunk and traveling branches. The free surface deformation is observed to transform with the change of the applied temperature difference. which manifests that the thermocapillary convection is sensitive to the temperature difference. Moreover, taking the temperature distribution into account. it is noted the deformation is formed in the colder area of the melt. The deformation of the free surface, which is characterized as a main trunk, would reach a maximum with the rise of the applied temperature difference. The oscillatory frequency of the main trunk, which is also sensitive to the applied temperature difference, increases with the rise of temperature. (C) 2004 Elsevier B.V. All rights reserved.