Pair Production of Fourth Family Charged Sleptons at $e^{+}{e}^{-}$ Colliders

We study the pair production of ${\tilde{l}}_4$, which is the supersymmetric partner of the fourth family charged lepton, at the $e^{+}{e}^{-}$ colliders. It is shown that the investigation of this process at ILC/CLIC will give opportunity to differentiate the MSSM with three and four families.