This paper aims to report genetic parameters and selection response for body weight at harvest of Nile tilapia (Oreochromis niloticus) over six generations of selection under salinity environment (15-20 ppt). The synthetic base population (G1) was formed in 2007 from three strains of Nile tilapia (O. niloticus), namely GIFT, Taiwan and NOVIT4 strains. Over six generations, a total of 25,294 individual fish which were offsprings of 475 male and 629 female brooders was performed data for selection. The estimate selection reponse for body weight at harvest by the mixed model was 22.7 percent. The high heritability (0.57) obtained for harvest body weight indicates that this population will continue responding to future selection.