A general study of the Seidel aberration properties of the flat slab lens systems made from left-handed materials was presented according to the primary aberration theory. Seidel aberration sums of such a system were derived based on the addition theorem. The way to find a flat slab lens system free from all five Seidel aberrations was described accordingly. Finally,two special examples of the singlet and doublet LHM slab lens systems without Seidel aberrations were given and discussed respectively.