We report on a search for B0s→μ+μ− and B0d→μ+μ− decays in pp collisions at s√=1.96  TeV using 364   pb−1 of data collected by the CDF II detector at the Fermilab Tevatron Collider. After applying all selection requirements, we observe no candidates inside the B0s or B0d mass windows. The resulting upper limits on the branching fractions are B(B0s→μ+μ−)<1.5×10−7 and B(B0d→μ+μ−)<3.9×10−8 at 90% confidence level.