Purpose To assess collagen content and types in the rectus abdominis muscle of cadavers of different ages. Methods Forty fresh adult male cadavers within 24 h of death were obtained from an Institute of Legal Medicine and divided by age at death into Group 1 (mean age, 23.3 years; range, 18–30 years; n  = 20) and Group 2 (mean age, 46.2 years; range, 31–60 years; n  = 20). From each cadaver, samples of the rectus abdominis muscle measuring 1 cm 2 were collected 3 cm superiorly and 2 cm inferiorly to the umbilicus. Histological sections were prepared and stained with picrosirius red and Masson’s trichrome stain for visualization of total collagen fibers, and immunohistochemical analysis was performed to distinguish types I, II, III, IV and V collagen. Results No significant differences in total collagen were found between groups by Masson’s trichrome staining. However, picrosirius red staining revealed a significantly greater amount and higher concentration of total collagen and types I and III collagen in Group 1 than in Group 2 ( P  < 0.05). All but type II collagen were detected by immunohistochemistry in both groups. No significant difference in type IV collagen was found between groups. Type V collagen was detected by immunohistochemistry in both groups, but quantification was not possible due to background staining. Conclusion The amounts of types I and III collagen in the rectus abdominis muscle were significantly smaller in older subjects.