There is a great demand for safe and effective alternative fumigants to replace methyl bromide and other toxic fumigants for postharvest pest control. Nitric oxide, a common signal molecule in biological systems, was found to be effective and safe to control insects under ultralow oxygen conditions. Four insect species including western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae); aphid, Nasonovia ribisnigri (Mosley) (Homoptera: Aphididae); confused flour beetle, Tribolium confusimi Jacquelin du Val (Coleoptera: Tenebrionidae); and rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae), at various life stages were fumigated with 0.1–2.0% nitric oxide under ultralow oxygen levels of ≤50 ppm in 1.9-liter glass jars at 2–25°C depending on insect species. Fumigations were effective against all four insect species. Efficacy of nitric oxide fumigation increased with nitric oxide concentration, treatment time, and temperature. There were also considerable variations among insect species as well as life stages in susceptibility to nitric oxide fumigation. Complete control of thrips was achieved in 2 and 8 h with 2.0 and 0.2% nitric oxide, respectively, at 2°C At the same temperature, complete control of the aphid was achieved in 3, 9, and 12 h with 1.0, 0.5, and 0.2% nitric oxide, respectively. Larvae, pupae, and adults of confused flour beetle were effectively controlled in 24 h with 0.5% nitric oxide at 20°C. Complete mortality of confused flour beetle eggs was achieved in 24 h with 2.0% nitric oxide at 10°C Rice weevil adults and eggs were effectively controlled with 1.0% nitric oxide in 24 and 48 h, respectively, at 25°C These results indicate that nitric oxide has potential as a fumigant for postharvest pest control.