Abstract: The present invention provides an optical fiber of which a zero dispersion wavelength falls within a range of between 1,250 nm and 1,350 nm inclusive, transmission loss at 1,550 nm is equal to or less than 0.185 dB/km, chromatic dispersion at 1,550 nm is within the range of 19±1 ps/nm·km, a dispersion slope at 1,550 nm is equal to or less than 0.06 ps/nm2·km, an effective area Aeff is equal to or more than 105 ?m2, a cable cutoff wavelength ?cc is equal to or less than 1,530 nm, polarization mode dispersion is equal to or less than 0.1 ps/km1/2, and a loss when the optical fiber is wound on a mandrel having an outer diameter of 20 mm is equal to or less than 10 dB/m.