We have performed a search for B0s→μ+μ− and B0→μ+μ− decays in pp¯ collisions at s√=1.96  TeV using 2  fb−1 of integrated luminosity collected by the CDF II detector at the Fermilab Tevatron Collider. The observed number of B0s and B0 candidates is consistent with background expectations. The resulting upper limits on the branching fractions are B(B0s→μ+μ−)<5.8×10−8 and B(B0→μ+μ−)<1.8×10−8 at 95% C.L.