A fast and simple method for analysis of trace amounts of Cr(III), Cu(II), Pb(II) and Zn(II) in environmental and biological samples was developed by combining magnetic solid phase extraction (MSPE) with inductively coupled plasma-optical emission spectrometry (ICP-OES) detection. Dithizone modified silica-coated magnetic Fe3O4 nanoparticles (H2Dz-SCMNPs) were prepared and used for MSPE of trace amounts of Cr(III), Cu(II), Pb(II) and Zn(II). The prepared magnetic nanoparticles were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). The factors affecting the extraction of the target metal ions such as pH, sample volume, eluent, and interfering ions had been investigated and the adsorption mechanism of the target metals on the self-prepared H2Dz-SCMNPs was investigated by FT-IR and X-ray photo electron spectroscopy (XPS). Under the optimized conditions, the detection limits of the developed method for Cr(III), Cu(II), Pb(II) and Zn(II) were 35, 11, 62, and 8 ng L−1, respectively, with the enrichment factor of 100. The relative standard deviations (RSDs, c = 10 μg L−1, n = 7) were in the range of 1.7–3.1% and the linear range was 0.1–100 μg L−1. The proposed method had been validated by two certified reference materials (GSBZ50009-88 environmental water and GBW07601 human hair), and the determined values were in good agreement with the certified values. The method was also applied for the determination of trace metals in real water and human hair samples with recoveries in the range of 85–110% for the spiked samples. The developed MSPE-ICP-OES method has the advantages of simplicity, rapidity, selectivity, high extraction efficiency and is suitable for the analysis of samples with large volume and complex matrix.Highlights► We prepared dithizone modified silica-coated magnetic Fe3O4 nanoparticles. ► A method of magnetic SPE-ICP-OES was proposed for trace heavy metal analysis. ► The developed method is simple, highly selective and sensitive. ► It is suitable for the analysis of samples with large volume and complex matrix. ► The adsorption mechanism was investigated by FT-IR and XPS.