Background. The diamondback moth [Plutella xylostella (L.)] is a major insect pest of cruciferous vegetables due to its infestation and resistance to pesticides. Pheromones have highly specialised advantages for each species and they leave no chemical residues. This study was an attempt to improve the understanding of the pheromone trap technique, a necessary step to produce safe vegetables in Vietnam. Material and methods. The investigations were conducted on cabbage (Brassica oleracea L. var. capitata) in Hanoi. Pheromone traps were used to catch adult diamondback moths every day and to count larvae on cabbage every 7 days. The data were analysed with Microsoft Excel 2007 and 146Conclusions. The larval density in the formula with pheromone traps was always lower than in the one without traps. Pheromone traps affected the density of larvae in the field. Not only do they bring more economic benefits than the use of pesticides only, but they also protect the environment and ensure the sustainability of ecosystems.