In-line measurement of the size and moisture content of particles using an optical displacement gauge and an infrared moisture meter was studied. In the field test of a salt manufacturing process, the mean predict error of the mean diameter of salt products in the range of 400-1,100 mum was 31 mum, and that of the moisture content in the range of 0.9-1.6% was 0.045%. As a result, the in-line prediction of the mean diameter and the moisture content of the salt product was realized. Therefore, it is concluded that this method can be applied to the process control of particulate products.