When high purity and large diameter are desired in manufacturing single crystals, defects due to “oscillatory thermocapillary” are inevitable in the crystal. The oscillatory convection is caused by “Hydrothermal wave instability”. We performed the tomographic stereo PIV on thermocapillary flows with thin liquid films for understanding the three dimensonal structure of Hydrothermal waves. As a result, the flow structure of Hydrothermal wave was captured and reconstructed sucsessfully.