A magnetic solid-phase extraction (MSPE) method was developed for the facile and sensitive determination of sulfadiazine prior to high-performance liquid chromatography (HPLC) analysis. The magnetic sorbent was prepared by the chemical co-precipitation of Fe3O4 magnetic nanocomposites modified with biochar. Characterization of the synthesized Fe3O4@BC-PN (Fe3O4 loaded pine leaves derived biochar) was performed by scanning electron microscopy - energy dispersive x-ray spectrometry (SEM-EDS), X-ray diffraction (XRD), vibrating sample magnetometry (VSM), and Brunauer - Emmett - Teller (BET) surface analysis. The saturation magnetization value was 17.95 emu/g by vibrating sample magnetometry. The Fe3O4@BC-PN particle sizes were determined to be 11.8 nm using the Debye-Scherrer relationship. The pH, mass of adsorbent, type, and volume of eluent were optimized. The limits of detection and quantification of the developed MSPE HPLC method were 10.7 mu g/L and 35.5 mu g/L, respectively. The intra-day and inter-day repeatabilities were below 4.2% and 7.7%, respectively. The developed method was employed to determine trace levels of sulfadiazine in spiked water samples.