A random distributed microstructure fiber in which strong asymmetry was introduced around a puresilica core was reported. Femtosecond laser pulses with duration of 35?fs from a Ti:sapphire laser oscillator were coupled into this fiber, and then periodic color rings were observed from the side of the fiber when the supercontinuum light propagated along the fiber. We attributed this phenomenon to the polarization beating of the supercontinuum light in this highly birefringent microstructure fiber. Measurement showed that the fiber had a beat length of approximately 1?mm at a central wavelength of 600?nm, which is in good agreement with the result of calculation. A new method is proposed to measure the beat length directly in a highly birefringent microstructure fiber.