  We calculate the branching ratio for the production of the meson $Y(4260)$ in
the decay $B^- \to Y(4260)K^-$. We use QCD sum rules approach and we consider
the $Y(4260)$ to be a mixture between charmonium and exotic tetraquark,
$[\bar{c}\bar{q}][qc]$, states with $J^{PC}=1^{--}$. Using the value of the
mixing angle determined previously as: $\theta=(53.0\pm0.5)^\circ$, we get the
branching ratio $\mathcal{B}(B\to Y(4260)K)=(1.34\pm0.47)\times10^{-6}$, which
allows us to estimate an interval on the branching fraction $3.0 \times 10^{-8}
< {\mathcal B}_{_Y} < 1.8 \times 10^{-6}$ in agreement with the experimental
upper limit reported by Babar Collaboration.
