Experiments were performed under low gravity condition in order to investigate the surface reaction model. A spherical platinum of 1.5 mm in diameter was used, and the surface temperature was measured by thermocouple. The mole fraction of nitrogen of the mixture was 0.91. As the effect of natural convection can be neglected under low gravity condition, the governing equations of mass, energy and species concentrations are formulated in one-dimensional polar coordinates. Axial symmetry, zero azimuthal velocity and no gradient along the axis are assumed. The low gravity condition of the present experiment was realized by the parabolic flight. The relative hydrogen concentration of the mixture was varied. If the relative hydrogen concentration is larger than 0.23, the numerical results simulated the experimental results successfully. However, at relative hydrogen concentration less than 0.23, the numerical results did not explain the experimental results well.