An optical fiber has a zero dispersion wavelength in a wavelength range of 1350 to 1410 nanometers; a dispersion of 2 to 8 ps/nm/km at a wavelength of 1550 nanometers; a dispersion slope of a positive value and not more than 0.05 ps/nm.sup.2/km at a wavelength of 1550 nanometers; a transmission loss of not more than 0.4 dB/km at a wavelength of 1380 nanometers; an increase of transmission loss of not more than 0.04 dB/km at a wavelength of 1380 nanometers after a hydrogen aging test; a transmission loss of not more than 0.25 dB/km at a wavelength of 1550 nanometers; and a bending loss of not more than 30 dB/m when the optical fiber is wound at a diameter of 20 millimeters at a wavelength of 1550 nanometers.