Two-phase motion of a cell inside a μ-channel is observed by the high-speed vision system. Two phases are defined as the phase of deformation and the phase of constant shape according to their characteristics. Red blood cells were used for experimental validation, and a mechanical model consisting of a spring and a damper in parallel is utilized for interpreting the behavior of the RBCs. An analysis method for acquiring the transition point between two phases is proposed, and is utilized in the analysis of the experimental results presented in this paper. Two different initial velocities of red blood cells approaching the μ-channel were used in the experiment. The experimental results show that the red blood cells with the higher initial velocity require longer distance to reach the steady state comparing to the ones with the lower initial velocity.