  We performed an analysis on the detection of a long-lived slepton at a linear
collider with $\sqrt{s}=500$ GeV. In GMSB models a long-lived NLSP is predicted
for large value of the supersymmetry breaking scale $\sqrt{F}$. Furthermore in
a large portion of the parameter space this particle is a stau. Such heavy
charged particles will leave a track in the tracking volume and hit the muonic
detector. In order to disentangle this signal from the muon background, we
explore kinematics and particle identification tools: time of flight device,
dE/dX and Cerenkov devices. We show that a linear collider will be able to
detect long-lived staus with masses up to the kinematical limit of the machine.
We also present our estimation of the sensitivity to the stau lifetime.
