Facing the large use of linseed as functional food, the presence of potentially toxic elements, and the matrix complexity, the development of alternative analytical methods is fundamental. Thus, the objective of this work is the development of a new method for the determination of cadmium, based on ultrasound-assisted extraction combined with supramolecular preconcentration followed by thermospray flame furnace atomic absorption spectrometry. A total of six samples of flaxseed flours of different brands and types were acquired (Brown Flaxseed and Golden Flaxseed). Cadmium (Cd2+) from samples was extracted, under previously optimized conditions, by ultrasound-assisted radiation in acid medium (1.5 mol L−1 HNO3) followed by liquid–liquid microextraction of the acid extract with dodecanoic acid/THF supramolecular solvent using diethyl dithiophosphate as the chelating agent. The method developed exhibited a detection limit of 0.1 ug L-1. The pre-concentration factor was 8.72 times, with intra and interday precision of 4.61 and 4.78% and accuracy and applicability when compared to conventional microwave-assisted digestion. Moreover, the results showed that the quantification of Cd2+ was not interfered with by ions commonly present in flaxseed capable of forming complexes in the pre-concentration stage. The cadmium concentration in the flaxseed flours was ranged from 0.11 ± 0.04 to 0.79 ± 0.03 µg g−1. Considering the maximum limit of 0.1 µg g-1 of cadmium for cereals, established by the European Food Safety Authority (EFSA) and the Food and Agriculture Organization and the World Health Organization (FAO/WHO), presence of Cd2+ in flaxseed flour samples was shown to be high. In conclusion, the method developed is reliable for quantifying cadmium and stands out for its low sample consumption, simplicity, low cost, in addition to being ecologically correct and fast. Considering the cadmium content found, the monitoring of toxic metals is extremely important to ensure quality control and benefits to human health.