Abstract: Two standard solutions of highly enriched isotopes of 162Dy and 164Dy were prepared from 162Dy and 164Dy in the form of oxides of well-defined purity. Gravimetric synthetic mixtures of two standard solutions were used to calibrate Finnigan MAT-261 Thermal Ionization Mass Spectrometer (TIMS). This instrument were used to determine isotopic abundance ratios on five natural samples of dysprosium to obtain an absolute isotope abundances of 0.056(2)at.% 156Dy, 0.095(2)at.% 158Dy, 2.329(12)at.% 160Dy, 18.889(28)at.% 161Dy, 25.475(24)at.% 162Dy, 24.896(28)at.% 163Dy and 28.260(36)at.% 164Dy. These absolute isotope abundances multiplied by their nuclear mass is equal to Dy atomic weight as 167.2591(9) with an uncertainty given on the basis of 95% confidence limit.