A new differential pulse polarographic (DPP) method has been developed for the trace determination of boron. Its most stable copper complex is used in 0.5 M KNO3 electrolyte since boron is not electroactive. By continuous addition of tetraborate to copper solution, the copper peak decreased first but then the peak became very small and nearly constant. This point was used for the boron determination. It was found that one mole of copper used two moles of tetraborate. Using this relationship, 1 x 10(-5) M tetraborate could be determined. The quantification limit was 2.5 x 10(-6) M and detection limit was 8 x 10(-7) M. In the presence of complex forming ions such as Pb, Zn, and Cd, the borate found in sample was somewhat smaller because of their reaction with borate. But since their complexes were not as strong as copper, only a few percent of borate were used. No interference was observed in the presence of calcium, chloride and sulfate. This method is applied for the determination of B in borax ore, waste water of borax industries and tap water of Ankara city.