This paper develops an analytical method of determining storage lengths of right-turn lanes at signalized intersections based on Queuing Theory Principle. The models of the storage length for two cases (Right-Turn-On-Red (RTOR) and No RTOR) are respectively developed, considering two situations: a. overflow: the right-turn vehicles overflow the lane and block the movement of the through-vehicles; and b. blockage: the queued through vehicles block the entrance of right-turn vehicles. The study investigates the effect of saturation ratio on the storage length to explore the influence of saturation ratio on right-turn length, and also provides the critical traffic volume for determination of the storage length. The impacts of saturation ratio and confidence level (the confidence probability of no-overflow or no-blockage) are also taken into account in this study, which has little considered in the existing references. Finally, the recommended storage lengths are obtained by modeling solution and verified through Vissim simulation. It is demonstrated that the obtained results are reasonable.