The present invention relates to a dispersionshifted fiber having a structure for effectively lowering polarization-mode dispersion. This dispersion-shifted fiber is a single-mode optical fiber mainly composed of silica glass and has a zerodispersion wavelength set within the range of at least 1.4 .mu.m but not longer than 1.7 .mu.m. In particular, at least the whole core region of the dispersion-shifted fiber contains fluorine.
