Two chemicals containing the active element deltamethrin selected for ULV spraying against Aedes aegypti which transmit dengue hemorrhagic were tested in Dong Da district, Hanoi. The results were that the two recommended dose by manufacturers with a preparation rate of 1-9 (1 part of chemical and 9 parts of water), DELAZONE MC and HANTOX - 200, produced good results with the mortality after 24 hours as follows: The knock-down rate was 97.5 percent, 99.5 percent, and 97.5 percent in the first time, second time and third time respectively. The testers and the people exposed to these two chemicals had been found no side effects.