The tribological properties of three different films commonly used in microelectromechanical systems (MEMS) under the lubrication of ionic liquid (IL)/water mixtures with various concentrations in the running-in process have been investigated. Results show that coefficients of friction (COFs) and wear rates for low temperature silicon oxide ( LTO)/Si3N4 vary in a similar way to the ones for poly-Si/Si3N4 under the lubrications of different IL/water mixtures. In contrast, the differences in COFs and wear rates are more significant in that the COFs and wear rates increase dramatically with the decrease in IL/water concentration in the case of self-mated Si3N4, while the differences in COFs and wear rates for the two other tribopairs are relatively small when the concentration is changed. The period of the running-in process reduces with the increase in IL/water concentration for all the tribopairs. Effective hydrodynamic lubrication can be found in the case of Si3N4/Si3N4 tribopair at higher IL/water concentrations without an evident running-in process, however, such a phenomenon cannot be observed for the other two tribopairs. Different wear mechanisms will also be analyzed in this paper. (C) 2009 Elsevier B.V. All rights reserved.