The effects of microbial transglutaminase (MTGase) on type I collagen self-assembly and properties of reconstructed collagen fibrils from shark were investigated. Collagen self-assembly was accelerated with the addition of MTGase in dependence on that concentration. The relative amount of reconstructed collagen slightly decreased with MTGase. The diffusion coefficient of collagen gel was reduced by treatment with MTGase, and that suggested the reduction of mobility of the whole collagen network. At a high temperature, used to denature the collagen, MTGase-treated collagen gel remained as aggregates. By differential scanning calorimetry, the denaturation temperature of MTGase-treated collagen gel was about 2 degreesC higher than that of nontreated collagen gel. Treatment with MTGase yielded thermally stable cross-links in collagen molecules.