In order to establish automatic landing technologies for a space plane, the Automatic Landing Flight Experiment (ALFLEX) was planned and 13 flights were carried out from July to August in 1996. As one of the research items of ALFLEX, we developed the Pseudolite DGPS System for ALFLEX and evaluated its function and ability to acquire the differential GPS technique for an automatic landing. We chose the pseudolite method for the ALFLEX DGPS system because of the simplification of the onboard system and the improvement of the geometrical dilution of precision (GDOP) at landing. On the other hand, the pseudolite method had some technical problems and had many newly developed elements. Although there were some dilfficulties with the development of the Pseudolite DGPS System, finally the system performed the efficient accuracy at the automatic flight experiment. This paper presents the evaluation results of the Pseudolite DGPS System for ALFLEX using real flight data of ALFLEX.