An experimental study is presented outlining the mechanical aspects of biological locomotion in beach fleas. Two basic types of dynamic behavior of beach fleas were examined, and their locomotive organs were observed microscopically. The jumping and swimming of beach fleas were analyzed by the high-speed video camera system. The structural properties of swimming and leaping organs were also studied. In the experiment for the jumping analysis, the relation between the surface roughness of ground and the horizontal jump distance were examined. Mechanical aspects in the relation between locomotive organs and behavior of beach flea were considered.