Calcination process is a method used for gamma rays mass attenuation coefficient enhancement of natural bentonite clay nano-particles. This process eliminates water and organic matter from bentonite clay structure which have low mass attenuation coefficient values. There are two opposite effects on mass attenuation coefficient values; oxides content increases after calcination process which enhances mass attenuation coefficient values and particle size of calcinated bentonite increases which decreases mass attenuation coefficient values. In order to enhance mass attenuation coefficient value for natural bentonite, a physical ball milling must introduced after calcination process that decreases particle size. Calcination process is done at 700 ̊C for two hours because dehydration is completed above 500 ˚C while dehydroxylation observed at 700 ˚C. Mass attenuation coefficients are measured for calcinated and ball milled bentonite clay at different energies (662, 1173 and 1332 keV) and different pressing pressures (50, 100 and 150 bar). Narrow beam transmission technique and two different sources (Cs-137 and Co-60) are used for mass attenuation coefficient measurements, also particle size are measured by two different methods dynamic light scattering and Williamson-Hall size analyses using XRD patterns. All samples are coated by polyvinyl alcohol polymer.