A novel fluorescent nanocomposite based on 6-amino-2-mercaptobenzothiazole (AMBT) was synthesized, characterized, and used as high-performance probe for detection of trace amounts of Fe3+ ions in water. The prepared AMBT-based ligand was grafted on Fe3O4@SiO2 nanocomposites, which provide both high surface area for hosting the ligand and easy magnetic removal of the nanoprobe from water. The prepared nanoprobe was characterized by X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, thermal gravimetric analysis, and vibrating sample magnetometer. Moreover, the designed nanocomposite showed spectroscopic colorimetric properties against low concentrations of Fe3+ ions in water. The detection limits of the probe for fluorometric and colorimetric detection of Fe3+ were 16.0 x 10(-9) M and 0.75 x 10(-6) M, respectively. Finally, the performance of the probe was tested in a natural water sample for detecting trace amounts of Fe3+. The theoretical calculations of the molecular structure for the designed organic ligand and its interaction with different ions confirmed strong binding energy of iron atom with thiol group of the ligand.