Influences of atomisation temperatures on the characteristic mass of thallium in the graphite furnace with the V-shaped boat were studied. The theoretical values of characteristic mass for thallium in the region of temperature (1800–2700 K) were calculated. The experimental results show that the calculated atomization efficiency (βa) of Tl in the pyrocoated graphite tube with the V-shaped boat and the Pd and the ammonium salt of EDTA as a matrix modifier is close to 100% for all temperatures (1800–2500 K). The analytical method on the basis of the calculated value of characteristic mass for the determination of thallium by furnace with the V-shaped boat using the Pd and the ammonium salt of EDTA as a matrix modifier is described. It was found that there were no interferences from 0.1 mol/dm3HC104, 40 μg/ml of Na (NaCl), Ca (CaCl2), Si (Na2SiO3) and K (KNO3) in the presence of 10 μg/ml Pd and 2% (v/v) ammonium salt of EDTA. The proposed method applied to determination of thallium in the drainage sediment and geochemical reference samples and the results of sample analyses were a good agreement with the expected values.