Using the data recorded in the National Genetic Evaluation System of the Australian Merino Breed (20,335 animals and 13,497 production records), the genetic parameters were estimate using restricted maximum likelihood methodology, applied to a multiple trait animal model for the five wool traits evaluated routinely:Greasy Fleece Weight (GFW), Clean Fleece Weight (CFW), Fibre Diameter (FD), Staple Length (SL) and Body Weight (BW). The heritabilities for these traits were 0.39, 0.39, 0.67 0.48 and 0.37, respectively. The genetic trend reached for FD by the national population and the selection nucleus (supported by INIA, SUL and SCMAU), was of -0.15 and -0.24 microns per year, respectively.