Disclosed is an electrolyte for a rechargeable lithium battery including a non-aqueous organic solvent, a lithium salt, and a lactam-based compound selected from the group consisting of compounds represented by formulas 1 to 6: ##STR00001## where R is a H radical, a C.sub.2 to C.sub.6 alkenyl or a halogen radical; and K, T, X, Y and Z are identically or independently H radicals or halogen radicals.