Abstract: The enhancement effect of double complexing agents on ytterbium is studied.Citrate, tartrate,EDTA, urea, and 5-sulfosalicylic acid are chosen as complexing agents. When the sum of the molar concentration of two complexing agents is kept constant as their ratio is varied, three types of enhancement effect, namely competitive, additive and synergistic, are found. The mechanism of the enhancement, the distribution of ytterbium atoms in the flame and the interferences of the concomitant elements and their elimination are studied. The sensitivity is increased to 0.15ppm/1% absorption. The results show that double complexing agents are more sensitive and selective for the determination of ytterbium than single complexing agents.