The mass attenuation coefficients of InSe and InSe having different holmium concentrations were measured in the energy region 15.746-40.930 keV using a Si(Li) detector. InSe and InSe:holmium(0.0025), InSe:holmium(0.0050), InSe:holmium(0.025) and InSe:holmium(0.05) crystals were grown by the Bridgman-Stocbarger method. The measured values are compared with the theoretical ones obtained using WinXcom which is a Windows version of XCOM. The measurement of mass attenuation coefficients of ternary semiconductors is very important because of its use in technology. (c) 2005 Elsevier Ltd. All rights reserved.