The effect of sunlight exposure on the mechanical properties of wool and wool/polyester fabrics was investigated. Instrumental analysis showed that the fabrics became stiffer, rougher, and less elastic with irradiation. This research revealed some differences compared with previously published results for wool fabric irradiated with an artificial light source. Subjective analysis suggested that changes in the mechanical properties can be detected at shorter irradiation times for 100% wool fabric than for wool/polyester fabrics. The hygral expansion of wool was unaffected by sunlight irradiation.