A model based on frustrated total reflection of waves in a multilayered medium has been developed to analyze the crosstalk between multimode optical fibers. Kappa (κ), the parameter indicating the power distribution among the modes of the fiber, and fiber cladding thickness play very important roles in determining the crosstalk isolation between fibers. Significant but less dominant effects on crosstalk are due to variations in fiber numerical aperture, length, and transmitting wavelength.