We have been performed on $Co^{60}$ ${gamma}$-ray irradiation of South Sea cultured pearls, with the absorbed dose of 0.1~100 kGy at room temperature. In addition, it was investigated electron paramagnetic resonance (EPR) and amino acid analysis (AAA) for detection of Gamma irradiated South Sea cultured pearls. It was observed that the irradiated South Sea cultured pearls revealed additional free radical peak such as $CO_2^-$, at a g-factor of $2.001{pm}0.002$ in EPR spectra. From the amino acid analysis (AAA), it was shown that some of amino acid in the protein of the nacre destroyed after ${gamma}$-ray; glutamic acid residue by 11.43 %, alanine by 3.11 %, and histidine by 43.75 %. It was useful to detect the irradiated South Sea cultured pearls by EPR measurement in our study.