The aim of this research is to present a method to evaluate the X-ray attenuation coefficient of (nano)particles by uniformly dispersing them in a host polymer, polydimethylsiloxane. The method is described and applied to the case of a material of interest for medical application in X-ray shielding and imaging, namely bismuth oxychloride nanoplates (BiOCl NP). A diagnostic X-ray machine was used to perform X-ray attenuation tests. A certified copper plate was used for calibration purposes and to find the X-ray photon energy. Blank polymer and composites were investigated, and the attenuation coefficient mu and the mass attenuation coefficient mu/rho of BiOCl NPs were found to be 45 cm(-1) and 6 cm(2) g(-1), respectively. Based on these values, a discussion is presented in which the perspective applications of BiOCl in medicine are discussed with specific focus on (i) X-ray shielding and (ii) X-ray imaging.