Alkaline pectinases could be applied in the bioscouring for cotton textiles to improve the wettability of the fabric. In order to evaluate the bioscouring effect of cotton fabrics directly and simply, the relationship between the amount of products degraded by alkaline pectinase and the wettability of the fabric was established with spectrophotometry. The results showed that products degraded by an alkaline pectinase Bioprep 3000L exhibited one characteristic absorption peak at 239 nm, which indicated that unsaturated degradation products were yielded. During the bioscouring of the cotton fabrics, the increase of the amount of both unsaturated degradation products and reducing sugars released from the pectins existing in raw cotton fiber was consistent with the improvement of wetting property of the cotton fabrics with prolonging the treatment time.