We perform the first search for lepton-number-violating B(+) -} D(-)l(+)l''(+) decays, where l and l'' stand for e or mu, using 772 x 10(6) B (B) over bar pairs accumulated at the Y(4S) resonance with the Belle detector at the KEKB e(+)e(-) collider. No evidence for these decays has been found.
Assuming uniform three-body phase space distributions for the D(-)l(+)l''(+) decays, we set the following upper limits on the branching fractions at 90% confidence level.B(B(+) -} D(-)e(+)e(+)) { 2.6 x 10(-6), B(B(+) -} D(-)e(+mu+)) { 1.8 x 10(-6) and B(B(+) -} D(-)mu(+)mu(+)) { 1.1 x 10(-6).