The characteristics of a Lyot optical fiber depolarizer had been investigated theoretically and experimentally. The formulas with respect to the degree of polarization and the corresponding parameters had been derived and discussed. The main specifications of the PANDA optical fiber used in the experiment were as follows: loss was 2.7 dB/kM, cut off wavelength was 1.12 micrometer and working wavelength was 1.3 micrometer. Experimental results verify the validity of this depolarizer architecture. A depolarizer with a degree of polarization of 2.0% has been obtained.