To investigate the effect of TiB2 particle size on the arc erosion behaviors of Ag-4wt.% TiB2 contact materials, ultrafine TiB2 powders were prepared by reactive ball milling with the mixture of Mg, B2O3 and TiO2 powders followed by acid wash. The phase constituents, size and morphology of the powders prepared were characterized by X-ray diffractometer (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Two kinds of Ag-4wt.% TiB2 contact materials were subsequently consolidated by powder metallurgy using ultrafine TiB2 powders and coarse TiB2 powders. The microstructure of Ag-4wt.% TiB2 contact materials was characterized, and the relative density, hardness and electrical conductivity of AgTiB2 contact materials were determined utilizing Archimedes method, a hardness analyzer and an eddy electrical conductivity gage, respectively. The arc erosion of Ag-4wt.% TiB2 contact materials was tested, the surface morphologies of Ag-4wt% TiB2 contact materials after arc erosion were characterized by scanning electron microscopy, the spatial distribution of TiB2 particles in Ag matrix was evaluated, and the arc duration and mass loss before and after arc erosion were determined as well. The results show that the relative density, electrical conductivity and hardness of Ag-4wt% TiB2 contact materials consolidated using ultrafine TiB2 powders are 85.45%, 55.17% International Annealed Copper Standard and 49.20 Brinell Hardness, respectively. Compared with the Ag-4wt.% TiB2 contact material consolidated using coarse TiB2 powders, the Ag-4wt.% TiB2 contact material prepared by ultrafine TiB2 powders presents shallower arc erosion pits, larger erosion area, more uniform dispersion and shorter arc duration. (C) 2014 Elsevier B.V. All rights reserved.