Amino acids are the building blocks of proteins, which are the most abundant macromolecules in living cells. From the standpoint of the photon interaction cross sections of amino acids, the mass attenuation coefficients, half and tenth value layers, mean free path, effective atomic and electronic cross sections, effective atomic number, and effective electron density of fifteen essential amino acids have been determined for 133Ba, 137Cs, and 60Co gamma-ray sources. The MCNP-4C code and the XCOM program have been used to calculate these parameters. The results have been compared to the avail-able experimental and theoretical data. The theoretical results agreed with the experimental data, with RD values of≤± 7％. In the energy region of 81–1332.5 keV, it was found that the μm, σa, and σe values of the amino acids decreased as the photon energy increased, and the increasing density of amino acids had no steady effect on these quantities. Additionally, results demonstrated that the HVL, TVL, and MFP values increased with the increase in photon energy. Theμm,σa, and Zeff values of aspartic acid were the highest among those of all amino acids, and they were the lowest for isoleucine. The Zeff value of each sample containing H, C, N, and O atoms was nearly constant in the studied energy region. The Neff values of the studied amino acids varied in the range of 3.14 × 1023–3.44 × 1023 electron/g. Furthermore, the Neff values were approximately independent of the amino acid type in this energy region.