A simple optical technique is described for the measurement of complex mode amplitudes in multimode fibers. The technique used in this experiment involves launching a laser beam into the core of low moded optical fiber, exciting a mixture of normal modes. The emerging mode patterns are stored in microcomputer. The complex modes are then extracted from these recoded intensities with help of modified version of Gerchberg-Saxton algorithm. Many experimental results are recorded in photographic form and comparison with computer analyzed pattern is made. The evaluation of complex mode amplitudes in multimode fiber can yield useful information about the mode filling of such fiber.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.