The ATLAS Experiment has conducted a search for the rare decays of $B_s$ and $B_d$ into two muons. $25$ fb$^{-1}$ of integrated luminosity of proton-proton collisions collected during LHC Run 1 were studied and new results were obtained, as presented in this talk. An upper limit is set on the branching ratio of $\cal{B}$($B_{d} \to \mu^+ \mu^-) < 4.2 \times 10^{-10}~\text{at}~ 95\%$ confidence level. For $B_s$, ATLAS measurement yields the branching ratio $\cal{B}$($B_{s} \to \mu^+ \mu^-) = (0.9^{+1.1}_{-0.8}) \times 10^{-9}$. The result is consistent with the Standard Model expectation and other available measurements.