Thirteen premenopausal women with stress urinary incontinence (SUI), 6 with SUI and prolapse, 9 with prolapse, and 19 without prolapse were enrolled to observe the content change of collagen type III and the expression of decorin mRNA in paraurethral connective tissues. Collagen type III from transvaginal biopsies was assayed by immunohistochemical staining and decorin mRNA was detected by real-time PCR. Premenopausal women with SUI had a significantly decreased level of collagen type III. Decorin mRNA expression was significantly increased in both premenopausal SUI+prolapse group and premenopausal prolapse group reflected by the decrease of DeltaCt value compared to their corresponding controls. The results suggest that a high level of decorin mRNA might be associated with the reduced content of collagen type III, resulting in a less flexible form of extracellular matrix in the connective tissue in SUI and prolapse patients.