In this study, opossum shrimps were introduced to elucidate propulsion mechanism of small aquatic creatures by ciliated pleopods. A pleopod was simplified to a straight cylindrical stem of 1.0mm in length and 0.1mm in diameter with 10 much narrower cylinders perpendicularly projecting on its either side to mimic the cilia. Flow resistance acting on the pleopod in a uniform flow, which corresponds to the propulsion force in rowing it, was computed, and it was found that the resistance decreased when interval between the adjacent cilia was below 0.4 mm.