This study aimed to investigate the rheology of two-mineral mixture systems as a function of pH and solid concentration. Single minerals (nickel oxide, quartz and hematite) and two-mineral systems (nickel oxide-quartz and nickel oxide-hematite) were studied. Rheology tests were conducted to investigate the effect of pH and solid concentration on shear yield stress of suspensions while zeta potential measurements of suspensions were used to explain the rheology results. Rheology results indicated that single mineral experiments showed that 5 and 10 vol.% of quartz and hematite had no shear yield stress whereas the one of nickel oxide was positive value. Shear yield stress of nickel oxide-quartz mixture and nickel oxide-hematite mixtures increased as increasing pH and solid concentration, and the value was higher than the one obtained with only nickel oxide. These results obtained with two-mineral mixture systems were explained by electrokinetic properties of the minerals, i.e. zeta potential of the minerals. (C) 2011 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.