Abstract With the aim of identifying QTL affecting wool production and wool quality in Merino sheep, specific regions of chromosomes 3, 4, 11 and 25 were analyzed in eight half-sib families, with an average of 63 offspring per sire. Greasy fleece weight and body weight were recorded at hogget and adult shearing. Individual mid-side fleece samples were collected to measure seven wool traits. The regression interval mapping analysis evidenced QTL related to fiber diameter on chromosome 3, on the region of type II keratin genes (KRT2) and fleece weight on chromosome 4, both in two families. We detected a QTL segregating for yield on chromosome 25, being the first description of QTL related to this trait. A second QTL was found for coefficient of variation of fiber diameter, in concordance with previous references. These results contribute to the understanding of the variability of wool traits. The reduction of the confidence intervals for QTL positions, would allow including them on marker-assisted selection schemes accelerating genetic progress of wool sheep.