An express post parcel was confiscated due to the stuff was not equal to the named stuff. HPLC coupled with high resolution mass spectrometry (HRMS) was applied to separate and elucidate the unknown by the combination of the accurate molecular weight, isotope ratio, and fragments. Nuclear magnetic resonance spectroscopy was performed for further confirmation. A new derivative of pesticide chlorantraniliprole was found and first reported. The pesticide analogue named 3-Bromo-1-(3-chloro-2-pyridinyl)-N-[2,4- dichloro-6-(isopropylcarbamoyl) henyl]-1H-pyrazole- 5-carboxamide. The derivative of chlorantraniliprole was not able to be detected by any routine pesticide residue analysis. It could be illegally used in claimed organic food or any natural vegetable. Besides, the dishonest people import illegal chemical through express post parcel without registering to any authority, made hazardous chemical transportation management very hard, as well the prevention of the entry of chemicals into food chain.