With the object of developing a new measuring method of the heat transfer coefficient at the inside wall of an agitated vessel in high Reynolds number region, extensive investigation has been conducted using a model tank that holds two types of thermocouples attached on the surface wall of a test piece. This new method is verified experimentally by the confirmation on the linearity of temperature slope in the test piece, suitability of setting method of the thermocouples on the surface of the test piece and the correspondence between this new method and the extrapolation method. Then, this new method is practically applied to determine the heat transfer coefficient at the inside wall of an agitated vessel. The impellers used are a 3-bladed propeller, a 4-bladed pitched paddle, a 6-bladed flat turbine and Satake Supermix MR210 as a large scale impeller. The characteristics of each impeller are clarified by investigating the effects of the impeller speed, baffling conditions, and the clearance between the impeller and the vessel bottom on the heat transfer coefficient. Moreover, new information concerning the relations between the flow pattern and the flow velocity distribution on the heat transfer coefficient are also clarified. Finally, this new method is confirmed to provide beneficial information for new designs of mixing devices.