This paper examines codend size selectivity in the Chilean hake (Merluccius gayi gayi) industrial fishery by means of four mesh sizes opening in the codend (100, 110, 130 and 140 mm mesh openings) and using the cover codend method. The data was analyzed by haul, using the SELECT model with both the Logistic and Richards selection curves. For each mesh size opening and sex the combined haul analysis was made with the Fryer model, and with these results we determine the Master Curves, by sex. Based on critical length and maturity length at 50% estimated for this specie we determined the optimum mesh size opening for the trawl fishery. The rate of escape of cmomon hake increased exponentially with the size of mesh opening. The Logistic selection model was chosen based on the likelihood ratio test for all hauls analyzed. From the mean selection curves (incorporating haul variation) fitted to data for combined sexes, the total length of 50% retention (l50) were estimated to be 39.3, 39.7, 41.1 and 43.6 cm of total length for 100, 110, 130 and 140 mm of mesh size opening. The values of l50 for females were higher than those for males. We recommended 120 mm of mesh size opening in the codend in order to protect the spawning fraction of Chilean hake stock and maximize the biomass of the cohorts