In this study, a dispersive liquid-liquid microextraction method based on a deep eutectic solvent (DES) combined with ultrasound assistance (as a substitute for the disperser solvent) has been developed for the preconcentration and determination of nickel ions in water and food samples. A deep eutectic solvent composed of choline chloride and 3,4-dimethylphenol in a 1:2 molar ratio was synthesized and used as the extraction solvent. Dimethylglyoxime was employed as a chelating agent to form a hydrophobic complex with nickel. Final measurements were carried out using flame atomic absorption spectrometry (FAAS). Various parameters affecting the extraction efficiency, including sample pH, DES volume, ligand concentration, ultrasonication time, centrifugation speed and time, ionic strength, sample volume, and the effect of interfering ions, were investigated and optimized. Under the optimal conditions, the calibration curve was linear in the range of 5–150 µg L⁻¹ with a correlation coefficient of 0.9986. The limit of detection was 1.4 µg L⁻¹, the relative standard deviation was 2.4 %, and the preconcentration factor was 50. The proposed method was successfully applied for the determination of nickel in real water and food samples, with recovery percentages ranging from 94 to 106%. The results indicate that the developed method exhibits good sensitivity, precision, and selectivity, and can be employed as an efficient approach for the determination of trace amounts of nickel in environmental and food samples.