An optical waveguide (optical fiber, for example) having low transmission loss, nonlinearity, and chromatic dispersion and facilitating the termination work for its end portions. An optical fiber 10 comprises a main medium 11 in which minute regions 12 composed of a multitude of submedia are distributed. The main medium 11 is made of silica glass, for example. The submedium in each minute region 12 is formed by a vacuum or a gas, such as an inert gas or air. The submedia have a refractive index smaller than that of the main medium 11. Each minute region 12 does not extend along the axis C.