Photon interaction (ZPIeff) and photon energy absorption (ZPEAeff) effective atomic numbers have been computed for some amino acids, namely, alanine (C3H7NO2), arginine (C6H14N4O2), aspartic acid (C4H7NO4), glycine (C2H5NO2), isoleucine (C6H13NO2), serine (C3H7NO3), and valine (C5H11NO2) in the energy range of 1 keV to 20 MeV. It has been observed that the effective atomic numbers (photon interaction and photon energy absorption) for the selected amino acid differ only in the lower-energy region (5 to 100 keV) and the maximum deviation is observed at ˜30 keV. Further, the maximum values of the effective atomic numbers for photon interaction and photon energy absorption were observed to be at different energies. For the photon interaction effective atomic number, the maximum for the selected amino acids appears at ˜5 keV, whereas the photon energy absorption effective atomic number has its maximum for the selected amino acids at ˜15 keV. Among the selected amino acids, aspartic acid shows the maximum effective atomic number, whereas the least effective atomic numbers were observed for isoleucine.