Monochromatic excitation X-ray fluorescence (ME-XRF) spectrometry emerges as a novel technique in trace element analysis, distinguished by its simplicity, rapidity, and efficiency. Its application in forensic toxicology has grown significantly for identifying toxic trace metals in biological samples. This study further expands its utility by developing a method for the rapid determination of arsenic (As), mercury (Hg), thallium (Tl), and lead (Pb) in hair samples. Calibration curves were established using analytical reference samples, and optimal detection conditions were determined and validated. The LODs for As, Hg, Tl, and Pb were 0.03, 0.03, 0.03, and 0.05 μg g