Alkali superoxide CsO₂ is one of the candidates for the spin-1/2 one-dimensional (1D) antiferromagnet, which may be sequentially formed by an ordering of the π-orbital of O₂ ^- molecule below T_S ̃ 70 K. Here, we report the magnetism and the high-magnetic field magnetization in pulsed-magnetic fields up to 60 T in powder CsO₂. We obtained the low temperature phase diagram around the antiferromagnetic ordering temperature T_N = 9.6 K under the magnetic field. At T = 1.3 K, we observed a remarkable up-turn curvature in the magnetization around a saturation field of ̃60 T, which indicates the low-dimensional nature of the spin system. The saturated magnetization is also estimated to be ̃1μ_B, which corresponds to spin-1/2. In this study we compare it with the theoretical calculation. <P />...