A new simple method is proposed for evaluating the magnetic antenna factor of an electrically small loop antenna. Generally the magnetic antenna factor is defined in far field condition. However it is difficult to realize the far field condition and propagate electromagnetic waves by electrically small antennas when the frequency range is less than 30MHz. Though some methods are proposed before, they have difficulty to realize the abovementioned matters. In the proposing method, the magnetic antenna factor of a loop antenna can be evaluated only by measuring the input impedance and loop radius because an electrically small loop antenna's characteristic is dominated by Faraday's law and the impedance in the relevant frequency range. So the evaluation does not need to require quantities related to other transfer characteristics of transmitting and receiving antennas.