A dispersion compensating fiber, which has a negative dispersion slope with a large absolute value while maintaining the absolute value of the chromatic dispersion, and which has sufficient dispersion slope compensation properties even for the non-zero dispersion shifted optical fiber requiring a large RDS for dispersion compensation. In this dispersion compensating fiber, the radius of a ring core region is set in a range from 6.7 m to 10.7 m, the radius ratio of a depressed core region relative to a central core region is set in a range from 2.0 to 3.0, and the radius ratio of the ring core region relative to the depressed core region is set in a range from 1.3 to 2.0, the relative refractive index difference of the central core region relative to the cladding is set in a range from +1.00% to +1.80%, the relative refractive index difference of the depressed core region relative to the cladding is set in a range from -1.20% to -1.50%, and the relative refractive index difference of the ring core region relative to the cladding is set in a range from +0.20% to +0.50%.