In order to select halophilic microorganisms as a source of compounds with cytotoxic activities, a total of 135 bacterial strains were isolated from water and sediment samples collected from the Zipaquirá salt mine in the Colombian Andes. Among these, we evaluated Labrenzia aggregata strain USBA 371, isolated from a saline spring in the Central Mountain Range in the Colombian Andes. This strain is a halophilic Alphaproteobacterium with high cytotoxic activity. This activity was associated with the production of diketopiperazines (DKPs) obtained from its extracellular fraction.