Three cannulated, multiparous dry cows were randomly assigned to a 3×3 Latin square experiment to evaluate the effects of different lucerne hay particle size on eating behaviour, chewing activity, and rumen fermentation based on measurements of the Penn State Particle Separator. During each of the 21-d periods, animals were offered one of three total mixed rations, which were chemically identical but included lucerne hay of different length (2, 4, 8 cm). Results showed that increasing lucerne hay particle size decreased intake of DM and NDF, increased chewing activities, rumen pH and ammonia concentration, and decreased the concentration of VFA.