An optical fiber has a core region and a cladding region surrounding the core region. The core region and the cladding region are made of a base material containing silica glass as a principal component. A plurality of holes extending along an axial direction are arranged at least in the cladding region. In the optical fiber, the base material has a hydroxyl mole fraction of not less than 10 ppm, or a fluorine content of not less than 0.2% by weight.