To explore environmentally friendly and benign solvents to capture NO gas, a series of ionic liquids was newly synthesized by 1,3-dimethylurea and tetrabutylphosphonium bromide with different mole ratios (1:1, 2:1, and 3:1). In addition, their NO absorption and desorption properties were studied at a temperature from 30 to 70 degrees C and atmospheric pressure for the first time. These synthesized ionic liquids exhibited excellent reversibility and high NO solubility, such as 1.173 mol of absorbed NO/mol of ionic liquids (3:1) at 40 degrees C and 101.3 kPa. The solubility of NO in these synthesized ionic liquids increased with the increase of the mole ratios of 1,3-dimethylurea in ionic liquids and also with the decrease of the temperature. The studies of Fourier transform infrared spectroscopy (FTIR) and H-1 and C-13 nuclear magnetic resonance (NMR) spectra revealed that it is a reversible chemical process for these ionic liquids to capture NO gas; therefore, we proposed a reversible chemical absorption mechanism. These reversible and benign ionic liquids potentially offer a new opportunity to absorb NO gas.