The characteristics of air plasma are studied using laser-induced breakdown spectroscopy at room temperature in air at atmospheric pressure. The electron temperature of 20796 K is determined using the Boltzmann plot method with six ionic nitrogen lines at 444.703, 463.054, 500.515, 566.663, 594.165, and 648.205 nm. The electron number density inferred by measuring the Stark broadened profile of well-isolated Hα line (656.273 nm) is 1.83 ￡ 1017 cm?3. The hypotheses of the local thermodynamic equilibrium and optically thin plasma are verified based on the experimental results. These results are beneficial for better understanding of the terahertz (THz) wave generation in pulsed laser induced air plasma.