An optical fiber includes a core, a clad having a plurality of air holes at a periphery of the core, and a hardening resin filled in a sealed portion at an end of the plurality of air holes. The hardening resin after hardening has a fill length of 7 mm to 8 mm. An optical fiber connection structure includes the optical fiber with an end face butt-connected to another optical fiber. An optical connector includes the optical fiber, and a ferrule to which the optical fiber is attached.