We have found that dialysis of S mg/mL collagen solution into the phosphate solution with a pH of 7.1 and an ionic strength of 256 mM at 25 degrees C results in a collagen gel with a birefringence and tubular pores aligned parallel to the growth direction of the gel. The time course of averaged diameter of tubular pores during the anisotropic gelation was expressed by a power law with an exponent of 1/3, suggesting that the formation of tubular pores is attributed to a spinodal decomposition-like phase separation. Small angle light scattering patterns and high resolution confocal laser scanning microscope images of the anisotropic collagen gel suggested that collagen fibrils are aligned perpendicular to the growth direction of the gel. The positional dependence of the order parameter of the collagen fibrils showed that the anisotropic collagen gel has an orientation gradient.