Laboratory studies were conducted to develop ultralow oxygen (ULO) treatment for controlling western flower thrips,Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), on broccoli at a low temperature of 1°C. Complete control was achieved in 5 d at 0.003% oxygen. Oxygen level affected efficacy of ULO treatment. At a higher oxygen level of 0.03%, 6-d treatment killed ≈85% of thrips, and 10-d treatment killed all thrips. The 5-d ULO treatment with 0.003% oxygen was successfully tested on iced commercial broccoli of several cultivars without any noticeable negative effects on shelf-life and postharvest quality. The ULO treatment provided a safe and effective alternative to methyl bromide fumigation for postharvest control of western flower thrips on exported broccoli for industrial development.