The unconventional halotolerant yeast Debaryomyces hansenii is of great importance in biotechnology and the food industry, and in basic research it serves as a model for studying the molecular mechanisms of resistance to increased salinity and osmotic stress. We have previously established an efficient method for editing the D. hansenii genome using the CRISPR/Cas9 system. In turn, this has stimulated further investigation of the structure and physiological role of DNA double-strand break repair pathways in D. hansenii. The aim of the present work was to evaluate the involvement of key components of the DNA double-stranded break repair system by the non-homologous end joining (NHEJ) mechanism in the resistance of D. hansenii to DNA-damaging compounds and compounds that induce oxidative, high salinity, and osmotic stress. Using the CRISPR/Cas9 system, mutant strains with knockout of the DEHA2F10208g (DhKU70), DEHA2B01584g (DhKU80) , and DEHA2G04224g (DhLIG4) genes encoding key components of NHEJ were obtained. It was found that mutant strains, unlike the wild-type strain, are sensitive to chemical compounds that damage DNA, as well as to compounds that cause oxidative stress. Osmotic and high salinity stresses and vanillin do not cause significant changes in the rate of colony formation of mutant strains. Unexpectedly, mutant strains exhibit increased resistance to caffeine compared to the wild-type strain. The data indicate that the NHEJ systems of D. hansenii play a significant role in the response to DNA-damaging and oxidative types of stress. The importance of the NHEJ system in the processes of maintaining yeast cell homeostasis should be taken into account when creating strains producing valuable substances.