Constraints on Unparticles from B_stoμ^+μ^-

Unparticle contributions to the recently measured decay mode $B_s\to\mu^+\mu^-$ are analyzed. We consider only the scalar unparticles because vector unparticles are expected to provide negligible contributions. Assuming that the relevant coupling constants are real, we present allowed regions of coupling constants and the scaling dimension of the scalar unparticle. While the measured value of the branching ratio is very close to the standard model predictions, one cannot exclude the possible contributions from unparticles.