AIM: We hypothesized that the loss of structural integrity in vessels of brain arteriovenous malformations (bAVM) is associated with abnormal expression of collagen subtypes. MATERIAL and METHODS: We retrospectively obtained the nidus tissue specimens from 24 bAVM patients and structurally normal cerebral cortex from six surgical epilepsy patients. The samples were paraffin-embedded and stained with Victoria blue and picrosirius red and examined by light microscopy. RESULTS: Light microscopy showed that collagen fibers became disorganized, and the internal elastic lamina was duplicated or interrupted in the arteries from the nidus tissue of bAVM. In some vessels in the nidus, Coil was the only collagen component and the interstitial tissue was mainly comprised of Coil. bAVM patients showed significantly higher Coil levels (86.25%+/- 13.92) and lower Col III levels (13.75%+/- 13.92) in the vasculature in the nidus tissue than those of otherwise normal surgical epilepsy patients (Col 1,80.78%+/- 18.03; Col III, 19.22%+/- 18.03) (p<0.001). Additionally, bAVM patients showed a higher Col I / Col III ratio (24.71 +/- 40.47) than that of normal controls (16.04 +/- 31.28) (p<0.001). CONCLUSION: bAVM patients exhibit changes in the Col I/Col III ratio and elastic fibers in the vasculature, which may compromise the structural integrity of cerebral vessels.