  Based on 3.26 fb$^{-1}$ data sample collected at CLEO III, we study the decay
$\tau^-\to K^+K^-\pi^-\nu_\tau$, and improve the measurement of the branching
ratio ${\cal B}(\tau^-\to K^+K^-\pi^-\nu_\tau)=
(1.59\pm0.06\pm0.13)\times10^{-3}$, the results are preliminary.
