Manganese substituted hydroxyapatite nanoparticles (nMnHAp) were produced using the ultrasonic wet chemical method. The elemental analysis was performed using Scanning Electron Microscopy (SEM) with integrated Energy Dispersive X-ray Spectrometry (EDX). The mass attenuation coefficients of manganese substituted hydroxyapatite nanoparticles have been measured at 59.5 keV gamma energy emitted from Am-241 radioisotope annular source with 50 mCi activity by using Ultra Low Energy Germanium Detector. These values are found to be in good agreement with theoretical values based on calculated XCOM data. Electron densities and effective atomic numbers were calculated by using the mass attenuation coefficients. Also, the mass attenuation coefficient of the real bone was determined as experimentally. The obtained results may provide information on how much radiation is transmitted through the sample when they are exposed to gamma-rays at 59.5 keV by comparing real bone.