Abstract: HNPC-A9012 is a novel tetronic acid derivative developed by Hunan Research Institute of Chemical Industry. The toxicity of HNPC-A9012 against different growth stages of Tetranychus cinnatarinus (Boisduval) were tested in laboratory by dipping method. The control efficacy against T.cinnatarinus and safety to cotton seedling were also evaluated. The LC50 value of HNPC-A9012 against alduts of T.cinnatarinus was 4.73 mg/L by slide-dip method, the LC50 value of HNPC-A9012 against eggs, nymphs and alduts of T.cinnatarinus were 10.91, 1.95 and 3.82 mg/L respectively by leaf-dipping method. The control efficacy of 20% HNPC-A9012 SC against T.cinnatarinus in potted plant were 81.64% and 92.12% at concentration of 60 and 80 mg/L, respectively, 21 days after treatment. The field control efficacy of 20% HNPC-A9012 SC against T.cinnatarinus in Shaanxi province were 92.59% and 95.64% at the dosage of 45 and 60 g/hm2, respectively, 21 days after treatment. Though the field control efficacy of 20% HNPC-A9012 SC against T.cinnatarinus in He'nan province was lower than that of Shaanxi province, it was similar to that of 240 g/L spirodiclofen SC and 15% pyridaben EC at the same dosage treatment. In addition, there was no crop injury observed at concentration of 80,160 and 320 mg/L.