The present invention relates to a nonlinear optical fiber which can generate a nonlinear optical phenomenon with high efficiency, an optical fiber coil wound with the nonlinear optical fiber, and a wavelength converter equipped with the nonlinear optical fiber. In particular, the nonlinear optical fiber according to the present invention has, as characteristics with respect to input light having a predetermined wavelength, a mode field diameter of 5 &mgr;m or less, a polarization mode dispersion of 1 ps/km½ or less or a fixed plane of polarization, a zero-dispersion wavelength of not less than 1.5 &mgr;m but not greater than 1.6 &mgr;m, a cutoff wavelength of not less than 1.4 &mgr;m but not greater than 1.7 &mgr;m at a length of 2 m, a transmission loss of 3 dB/km or less, and a nonlinear coefficient of 10/W/km or more. As a result of this configuration, the nonlinear optical fiber generates, with high efficiency, desirable converted light occurring upon the nonlinear phenomenon.