Background:The thread caterpillar Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae), is an insect pest that attacks the lettuce, Lactuca sativa and this is a serious problem faced by farmers in Niassa province due to the fact that at the end of the fourth larval stage it (insect) cuts saplings and compromising agricultural output. Usually the control of this pest has been done using synthetic insecticides, but these have environmental related implications. Thus the researches of eco-friendly forms of control have been studied. Methods:In this research, the lettuce intercropping with onion Allium cepa was carried out to control the insect pest A. ípsilon. The experiment took place at the Agricultural Research Institute of Mozambique-IIAM. Several trials, one in monoculture (only lettuce) and other intercropped with onion were performed. In the experiment different intercropping patterns were tested, namely: Surround (a continuous line of onion surrounding a lettuce line), alternating (a line of onion and another of lettuce) and two lines of lettuce and one of lettuce.Results: Based on tests conducted, the intercropping of lettuce with onion resulted in more plant not attacked after the test compared to the monocrop (only lettuce). In the same research we studied the best pattern to intercropping and it was found that the surrounding form (a continuous line of onion encircling a lettuce line), after the experiment, showed a higher average number of non-attacked lettuce plants. Conclusions:Surrounding was the best intercropping pattern because showed a higher average number of nonattacked lettuce plants. The current results indicate that the onion can be used as useful tool to control the caterpillar, A. ipsolon in lettuce.