Strontium-89 is an important radiotherapy nuclide in bone palliation. The standardization of 59Sr has been performed at the National Office of Measures (OMH) within the frame of the BIPM CCRI(II)-K2.Sr-89 key comparison. The activity concentration of the 89Sr solution was measured by two different methods. The conventional 4pi beta counting technique was used with two proportional counting measurement systems. The 4pi beta-gamma-coincidence efficiency tracing method was used with a 4pi beta-gamma-coincidence measurement system using 24Na as the tracer radionuclide. The beta efficiencies of each of these counting techniques were nearly 100%. The combined uncertainties of the activity concentration determined by these absolute methods are 0.3%. The general agreement of results between the two methods was 0.5%. The measurement equipment, evaluation methods and results of activity concentration measurements with their uncertainty budgets are reported.