The objective of this study was to evaluate the effect of Spirulina supplementation, sire breed and sex on the wool characteristics of purebred and crossbred Merino weaned lambs under a single pasture-based management system. Lambs sired by Merino, White Suffolk, Dorset, Black Suffolk breeds were randomly allocated into 3 treatments – the control group grazing without Spirulina (0 mL), low (100 mL) and high (200 mL) Spirulina groups. All lambs were kept as a single mob in paddocks, grazed for 9 weeks and wool samples analysed. Differences in wool quality between the control and supplemented groups were not significant (P>0.05). However, sire breed significantly (P<0.001) influenced fibre diameter, spinning fineness, comfort factor and fibre curvature with purebred Merinos having superior wool quality than crossbreds. Wethers grew higher quality wool than ewes. Spirulina has a potential as an alternative supplementary bioresource in dual-purpose sheep feeding because it does not compromise wool quality in supplemented weaner lambs.