Endosymbiotic bacteria Xenorhabdus and Photorhabdus spp. extracted from the entomopathogenic nematodes can be a promising tool for pest management strategies. The endosymbionts need to be screened for their biocontrol activities after their isolation. This chapter incorporates the methods for the isolation of entomopathogenic nematodes, their endosymbiont bacteria, and further their screening procedure. These screening methods are based on the various secondary metabolites secreted by the endosymbionts. Secondary metabolites such as ammonia, siderophores, hydrogen cyanide (HCN), and hydrolytic enzymes (amylase, chitinase, and proteases) attribute to the antimicrobial properties. Endosymbionts screened for biocontrol activities can play a pivotal role in the direction of sustainable agriculture and biological control.