In the cement industry, high pressure grinding rolls (HPGR) has been used since 1985. At the first applications, this equipment has been installed in the existing cement grinding circuits as an open circuit precrusher in order to crush clinker especially. The cement factories produce different type of cement by using basically clinker, gypsum and additives like limestone and trass. The additives generally are not precrushed before ball mill circuits. In this study, three different mixed feeds were prepared with clinker, gypsum, limestone and trass to evaluate the performance of an industrial scale open circuit HPGR. The results of the tests show that due to the stress concentrates on soft and fractured material, the performance of HPGR becomes worse when the relatively hard material (clinker) is fed together with soft and weak materials (i.e. gypsum, limestone, trass). In addition to the industrial tests, the piston die tests have been also performed with narrow size fractions of the mixed and unmixed materials. (C) 2010 Published by Elsevier Ltd.