Leg motion learning while walking backward with eyes closed on a treadmill was studied to gain information on self-organization in locomotion learning. Eight adults walked on a treadmill at a belt speed of 50 m/min for five minutes,, four times. The angles of the hip, knee, and ankle joints were calculated to describe lower limb motion transition with learning progress. The attractor of a dynamical system creating joint flexion and extension was reconstructed from time-series joint angle data by the method of Takens (1981). Main findings were that: 1) the joint motion transition pattern with learning progress differs for the three leg joints; 2) with learning progress, ankle joint motion converged from complex to a certain clear pattern and, as a result, the chaotic property of the joint became weak; and 3) with learning motion, the fractal dimension of the attractor for knee joint motion exceeded those for the ankle and hip joints.