There is disclosed an optical fiber wherein an absolute value of the fourth order dispersion .beta..sub.4 of fourth derivative .beta..sub.4 of propagation constant .beta. with respect to angular frequency .omega. at a mean zero dispersion wavelength .lamda..sub.0 in an overall length is not more than 5.times.10.sup.-56 s.sup.4/m and wherein a fluctuation of a zero dispersion wavelength along a longitudinal direction is not more than .+-.0.6 nm.