Experimental studies were made on particle size distribution of wood fibre ground by disk type refiner. Refiner used was Bauer type double rotating disk refiner sized 915mm in diameter.Particle sizes were measured by standard sieves and their distribution constants n were correlated with the densities of experimental woods. From the experiments, it was found that with increase of the apparent density of wood ρw decreases the value of n.Experimental relation was n=0.28ρw-1.2By the above relation, together with the experimental data on power consumed in disk type refiner, it became possible to evaluate the particle size distribution of wood fibre as a function of power consumption of disk type refiner.