There are many potential sites for geothermal power plants in Thailand. After many years of geological andgeophysical surveys, a pilot magnetotelluric (MT) survey was made to assess the reservoir of the Mae Changeothermal area, northern Thailand, which is one of the key areas for geothermal development. SevenMT sites were deployed in a 3 km × 4 km area around the Mae Chan district covering the Mae Chan hotsprings. The MT data were acquired at low and high frequency ranges and were inverted using a 3-D MTinversion to yield the 3-D resistivity structure of the area. The results show that there are two conductivezones near the surface associated with the hot fluid of the Mae Chan hydrothermal system. The hot fluidreservoir mostly resides at less than 500 m below the surface in weathered and fractured granite and inthe overlying sedimentary deposits. Its source rock is imaged as a resistive zone corresponding to the hotgranite batholith below it. The hot fluid rises up along the Mae Chan fault. The fault is clearly observed asa resistivity contrast extending from the surface to depth. It dips at a moderate angle. From the measuredtemperature of the fluid from a drill hole and the estimated temperature of the granite rock from theresistivity structure we conclude that the Mae Chan geothermal area is likely to be suitable for immediatedevelopment of a small-scale geothermal power plant.