For determination of the bandwidth of optical fibers, the invention proposes a method which comprises the injection of light at a first optical power level and at a first frequency into an optical fiber, as well as the measurement of a first signal level as a function of the optical power level of the light passing through the fiber at the first frequency, the injection of light at the second optical power level and at a second frequency into the optical fiber, the measurement of a second signal level as a function of the optical power level of the light passing through the fiber at the second frequency, and the determination of the bandwidth of the fiber as a function of the first and second optical power levels and/or of the measured first and second signal levels using a predetermined rule which describes the frequency-dependant attenuation response of the fiber.