Abstract: Photorhabdus luminescens and Xenorhabdus nematophila are entomopathogenic bacterial symbionts of beneficial nematodes Heterorhabditis bacteriophora and Steinernema carpocapsae, respectively. These bacterial symbionts are known to secrete an array of toxins, enzymes and antimicrobials that kill, bioconvert and protect the insect host for optimal nematode growth and reproduction. The present study explores heat stability of antibacterial metabolites secreted by X. nematophila. Permeate of a liquid X. nematophila culture was subjected to various sterilization treatments to observe the effects of heat sterilization on antibacterial activity. Activity was measured as bacterial sensitivity which is assayed utilizing a modified-version of the Kirby-Bauer disk diffusion method. Results demonstrate that X. nematophila produces both heat-labile and heat-stabile antibacterials that are effective against different species of bacteria. Results also indicated that heat-stabile components are more active than heat-labile components. The discovery of an environmental organism that produces both heat-stabile and heat-labile antibacterials can be exploited to manufacture these compounds for potential medical applications for human and animal use.