The work presented in this paper was part of a larger study on comminution of coal/biomass blends for cofiring applications in pulverised fuel coal-fired boilers. A series of laboratory-scale ball milling experiments were conducted as part of this investigation to study the milling characteristics of bituminous coal and hardwood chips blends. A mass-balance based size reduction model was also employed to gain a greater understanding of the co-milling behaviour of coal/biomass blends. Milling properties of the blends were studied for blending ratios (wt.% of biomass in the blend) of 0 wt.%, 3 wt.%, 5 wt.%, 10 wt.%, 50 wt.% and 100 wt.%. Results suggest that for blending ratios of up to 50 wt.% the output particle size distribution of the blend is the arithmetic average of the particle size distributions of the parent materials. Analysis of particles images also revealed that the two-dimensional "Roundness" shape factors for biomass and coal particles were distinctly different with mean values about 0.25 and 0.8, respectively. So too, the three-dimensional "sphericity" shape factors of the two materials were found to differ significantly. Values of 0.58 (biomass) and 0.86 (coal) were obtained from a correlation between the particle Roundness and sphericity. (C) 2012 Elsevier B.V. All rights reserved.