Calibration of electric field probes in a GTEM cell is carried out using the reference antenna method. To determine the effectiveness of the calibration, we compared our results with those of calibration in an anechoic chamber from 1 to 6GHz. Each electric field probe had three elements, one of which was used to calibrate the other two. The calibration factors in the GTEM cell agree well with those in the anechoic chamber. Therefore, the GTEM cell is as effective as the anechoic chamber for calibrating electric field probes with the same type of probe and helps save more measurement time and effort.