The effect of ozone on the reduction of chlorpyrifos residue in lychee cv. Chakapat (Litchi chinensis Sonn.) was studied. Lychee fruits were dipped in the solution of chlorpyrifos at a concentration of 10 mg L-1 for 10 min. Then, they were exposed to ozone gas (O3) at concentrations of 80, 160, 200, 240 mg L-1 and dipped in ozone- containing water, at concentrations of 2.2, 2.4, 3.4 and 3.2 mg. L-1 for 10, 20, 30 and 60 min, respectively. Both ozone gas and ozone-containing water reduced pesticide residue in lychee, but exposure to ozone gas for 60 min was most effective. When lychee fruits were stored at 25°C for 6 days, both processes did not show significant differences in weight loss, total soluble solids (TSS) and titratable acidity (TA). However, ozone-containing water decreased the eating quality of lychees after storage, compared with the ozone-fumigated groups. © 2011 International Ozone Association.