The new luminescence method for determining dysprosium in the presence of terbium is developed based on the difference in the lifetimes of dysprosium and terbium in complexes with 3-(6-benzodioxanyl)pyrazole-5-carboxylic acid (τ = 6 and 910 μs, respectively). The possibility of determining the short-lived and weakly luminescent dysprosium(III) ion in the presence of long-living and intensively luminescent terbium(III) was demonstrated for the first time using time-resolved luminescence. The developed method was used to determine dysprosium in luminescent materials doped with both lanthanides.