Collagen fibers self-assembled from solutions of molecular type I collagen were mineralized at pH 9.5, by exposure to super-saturated solutions of calcium and phosphate for a one week period in a double diffusion chamber. Uniaxial tensile mechanical properties increased with mineralization and electron microscopy of the mineral formed within the fiber was morphologically similar to the mineral phase of calcified tissues. Selected area electron diffraction confirms the presence of hydroxyapatite crystal. Further, the aligned fibrillar substructure serves as a template for the orientation of the c-axis diffraction maxima of the hydroxyapatite. These results indicate that an aligned system composed exclusively of selfassembled type I collagen fibrils serves as a scaffold for oriented growth of mineral analogous to calcification in vertebrate bone.