A new, simple, fast, and environmental friendly sample preconcentration technique based on the modified Fe₃O₄ nanoparticles has been developed for extraction, and determination of ochratoxin A (OTA). Magnetic nanoparticles were coated with 3-(trimethoxysilyl)-1-propanethiol and modified by ethylene glycol bis-mercaptoacetate. Transmission electron microscopy, X-ray diffraction, and Fourier transform infrared spectrometry were used to characterize the adsorbents and the main parameters affecting the extraction and desorption efficiencies, such as pH of sample solution, sample volume, desorption conditions, extraction and desorption times, salt addition, and co-existing interferences have been investigated and established. Under optimal conditions, OTA was extracted and analyzed using high performance liquid chromatography with fluorescence detection. The mobile phase consists of acetonitrile : water : acetic acid (99:99:2, v/v/v) and fluorescence detection was performed with excitation and emission wavelengths at 333 and 477 nm, respectively. An enrichment factor of 24 was achieved for OTA with relative standard deviation of <7%. The proposed method was applied to twenty samples of cereals (rice, wheat, and corn). The limits of detection of 0.06, 0.03, and 0.05 ng mL⁻¹ and limits of quantitation of 0.19, 0.11, and 0.15 ng mL⁻¹, were found for rice, wheat, and corn samples, respectively. The recoveries of OTA for spiked samples were ranged from 87 to 93%