standardized methodology was utilized to determine length and proportion of the different fibres,alcohol scouring yield, and histogram of diameter frequency distribution. Spanish Merino and Socorro Merino have square staples without long-coarse fibres, while Ibicenca showed a double coated fleece with long conical staples (15,2±5,1 cm); Grazalema Merino occupies an intermediate position (7,7±2,4 cm; P<0,01). Only short-fine fibres were found in the Spanish Merino, and they were significantly shorter than the three other breeds (3,2±0,6 cm; P<0,01). Proportion of short-fine fibres in Socorro Merino and Spanish Merino was higher (>98,5%) than in the Grazalema Merino and the Ibicenca (<79,2%; P<0,01), the latter with the highest amount of kemp (8,4±11,8%; P<0,01). Scouring yield was lower in Socorro and Spanish Merinos (52-52%) than in the other two breeds (75-77%; P<0,01). Diameter frequency histograms suggest that Socorro Merino has maintained the characteristics of the original flock of Australian Merino introduced into the Island in 1869. Grazalema Merino shows the influence of crosses with coarse wool breeds, while Ibicenca is the only one with a defined double coated fleece.