A dispersion compensating fiber module which, when connected to an optical fiber which exhibits, at a wavelength of 1.55 .mu.m, a chromatic dispersion of between +2 and +6 ps/nm/km, a dispersion slope of between +0.075 ps/nm.sup.2/km and +0.095 ps/nm.sup.2/pm, and a relative dispersion slope of between 0.016 nm.sup.-1 and 0.024 nm.sup.-1, performs compensation so that the residual dispersion of the connected optical fiber is reduced, the dispersion compensating fiber module includes a dispersion compensating fiber and at least one optical fiber fused to the dispersion compensating fiber, in which the dispersion compensating fiber module exhibits at a wavelength of 1.55 .mu.m, a relative dispersion slope of between 0.016 nm.sup.-1 and 0.026 nm.sup.-1; and in a wavelength range between 1.525 .mu.m and 1.565 .mu.m, a maximum residual dispersion difference, when converted per km of the transmission optical fiber, of less than or equal to 0.4 ps/nm/km.