In this report, an interferometric method for measuring the parameters of the emitted light from a Step-Index Single- Mode optical fiber is introduced. A mirror oriented normal to the optical fiber axis is axially scanned in front of the fiber emitting face. The intensity of the resultant coupled back into the fiber interference is then detected. Interference fringes are used, as a tool, to determine the emitted light modal radius. Knowing the beam waist, the values of other parameters of the beam can be calculated.