  We study the single production of fourth-family $t'$ quarks via the process
$ep\to t'\nu$ at Large Hadron electron Collider (LHeC). We calculate the
background and signal cross sections for the mass range 300-800 GeV. It is
shown that the LHeC can discover single $t'$ quark up to the mass of 800 GeV
for the optimized mixing parameters.
