An optical fiber has a core and a cladding that are made of silica-based glass. The optical fiber having a mode field diameter of 5.5 µm or larger at a wavelength of 1100 nm, transmitting light with a wavelength of 1250 nm in a single mode, and having a bending loss of 1 dB/turn or smaller at a wavelength of 1100 nm when the optical fiber is bent with a curvature radius of 2 mm. Thereby, an optical fiber and an optical fiber ribbon of which the bending loss and the connection loss are both reduced and that are suitable for easily constructing an optical interconnection system, and an optical interconnection system using these are provided.