Abstract <p><i>Halomonas campaniensis</i> XH26 is a wild-type bacterial strain that efficiently accumulates ectoine, a naturally occurring osmoprotectant. Strain XH26 was grown in the presence of four metal nanomaterials (MNPs), and their effects on intracellular ectoine accumulation were analyzed. Using optimal concentrations of the four MNPs (CuO, 6 mg/L; Fe₃O₄, 100 mg/L; ZnFe₂O₄, 450 mg/L; MnFe₂O₄, 550 mg/L), the intracellular accumulation of ectoine in strain XH26 was enhanced by 9.5, 54.9, 30.4, and 31.9%, respectively. Iron oxide NPs demonstrated a significant catalytic effect on intracellular ectoine accumulation. Intracellular oxidation and antioxidant experiments revealed that CuO NPs exhibited substantially higher toxicity compared to iron oxide NPs. Comparative metabolomic analysis of strain XH26 treated with 100 mg/L Fe₃O₄ NPs and the NP-free control revealed that the significantly different metabolites in the control group were fumarate, L-histidine, L-tryptophan, L-methionine, L-proline, and isocitrate. KEGG pathway enrichment analysis indicated that the significantly different metabolic pathways were primarily amino acid, energy, and carbohydrate metabolism. The results of metabolomic analysis indicated that the mechanism of resistance and adaptation of strain XH26 to the MNPs may be associated with the intracellular tricarboxylic acid cycle and the extent of ectoine accumulation.</p>