A chromatic dispersion compensating and dispersion slope compensating optical fiber comprises a central core having an index difference .DELTA.n.sub.1 with an outer optical cladding, a first buried inner cladding having an index difference .DELTA.n.sub.2 with the outer cladding, a ring having an index difference .DELTA.n.sub.3 with the outer cladding and a second buried inner cladding having an index difference .DELTA.n.sub.4 with the outer cladding. The index difference between the first buried inner cladding and the outer cladding .DELTA.n.sub.2 is less than or equal to -13.5.10.sup.-3 and the index difference between the second buried inner cladding and the outer cladding .DELTA.n.sub.4 is less than or equal to -3.10.sup.-3. The fiber has, for a wavelength of 1550 nm, a chromatic dispersion less than or equal to -50 ps/nm/km and a ratio of the chromatic dispersion over the chromatic dispersion slope DOS less than or equal to 70 nm. The second deeply buried inner cladding allows obtaining a low DOS value whilst maintaining acceptable optical characteristics.