ECT (Eddy Current Testing) and UT (Ultrasonic Testing) have been widely used for the non-destructive testing of metal structures. It is well known that these two techniques complement each other for crack sizing; ECT has a high capability of sizing of a surface breaking crack and UT is suitable for sizing of a sub-surface breaking crack in thick-wall structure. Based on these back-grounds, the authors have proposed a novel dual probe with simple structure that combining EMAT (Electromagnetic Acoustic Transducer) and EC (Eddy Current) probe. In this paper, the above dual probe is applied to monitoring of piping wall thinning in high temperature environment. For the purpose, the structure and components of the probe are discussed so that the present probe should withstand the operating temperature of up to 300 degrees C which corresponds to the operating temperature of boiling-water nuclear reactors. Finally, basic performance of the probe at high temperatures is investigated through experiment using an electric furnace.