The method of determining sound power levels of noise sources by the sound intensity technique has been specified in ISO 9614 Part 1 (precision, engineering, and survey grades by the discrete point method) and Part 2 (engineering and survey grades by the scanning method). In addition to these, the work of drafting, Part 3 (precision grade by the scanning method) has just started in ISO/TC43/SC1/WG25. In order to obtain data for the specification of the measurement accuracy of the scanning intensity method, a basic experimental study has been done. In this study, an artificial sound source (a loudspeaker array) with complicated sound radiation characteristics and two actual sound sources (a vacuum cleaner and a compressor) were used as the sound sources under test. The sound power level of each sound source was determined in each 1/3 oct band from 50 Hz to 6.3 kHz and those in the octave band and A-weighted values were calculated from the values in the 1/3 oct bands. From these results, the measurement repeatability, the influences of the field nonuniformity, and the temporal variability on the measurement accuracy, and the field indicators were investigated.