Optically transparent composite membranes have been made from two immiscible polymers, the biaxially drawn UHMWPE (the fiber, 80-400 mum in diameter) and the polyether polyurethane. The as-made composites have a volume fraction up to 24% and a light transparency up to 70%. The light transmission of all the composites tested is linearly dependent on the wavelength of the visible incident light. The slope (K) and the constant (C) derived from the linear relation were correlated with a mathematical model. The K-value changed with the changed of the residual voids in the composite. The C-value changed with the change of the refractive indices. The light transmission of the composite membranes can be optimized through the control of both K and C, preferably controlling the K-values. The highest light transparency was found in Toyobo TM5 composite heat compacted at 115 degreesC.