The lifetime of the metastable 5d$^2$D$_{5/2}$ state has been measured for a single trapped Ba$^+$ ion in a Paul trap in Ultra High Vacuum (UHV) in the 10$^{-10}$ mbar pressure range. A total of 5046 individual periods when the ion was shelved in thi
s state have been recorded. A preliminary value $tau_{D_{5/2}} = 26.4(1.7)$~s is obtained through extrapolation to zero residual gas pressure.
