An automatic method for classifying frequency shift keying (FSK), minimum shift keying (MSK), phase shift keying (PSK), quadrature amplitude modulation (QAM), and orthogonal frequency division multiplexing (OFDM) is proposed by simulta-neously using normality test, spectral analysis, and geometrical characteristics of in-phase-quadrature (I-Q) constellation dia-gram. Since the extracted features are unique for each modula-tion, they can be considered as a fingerprint of each modulation. We show that the proposed algorithm outperforms the pre-viously published methods in terms of signal-to-noise ratio (SNR) and success rate. For example, the success rate of the pro-posed method for 64-QAM modulation at SNR=11 dB is 99%. Another advantage of the proposed method is its wide SNR range; such that the probability of classification for 16-QAM at SNR=3 dB is almost 1. The proposed method also provides a database for geometrical features of I-Q constellation diagram. By comparing and correlating the data of the provided database with the estimated I-Q diagram of the received signal, the pro-cessing gain of 4 dB is obtained. Whatever can be mentioned about the preference of the proposed algorithm are low com-plexity, low SNR, wide range of modulation set, and enhanced recognition at higher-order modulations.