In order to elucidate AC loss characteristics of High-Tc superconducting coils wound by stacked conductors, we measured AC losses of Bi-2223 sample coils under the various electro-magnetic conditions by a nitrogen boil-off method. The sample coils were wound by stacked conductors, which were composed of two Bi-2223 tapes. Each tape of stacked conductors was wrapped with the polyimide tape, and two tapes were transposed at the end part of sample coils. The diameter of sample coils is about 50 mm, and the height is about 30 mm. We measured the frequency dependence and the magnetic amplitude dependence of AC losses of sample coils under external sinusoidal magnetic field, and evaluated the magnetization losses and coupling current losses. We also measured AC losses of sample coils under external square wave magnetic field using power electronic circuits. Based on the measured results, AC loss characteristics of High-Tc superconducting coils wound by stacked conductors were discussed.