We study the semileptonic branching fraction of B-meson into higher resonance of charmed meson D^<**> by using the Bjorken sum rule and the heavy quark effective theory(HQET). This sum rule and the current experiment of B-meson semileptonic decay into D and D^* predict that the branching ratio into D^<**>lν_l is about 1.7%. This predicted value is larger than the value obtained by various models.