Disclosed is a liquid crystal display device, comprising: a first substrate including a first alignment key formed thereon, the first alignment key having at least first and second alignment marks spaced from each other; and a second substrate to be aligned with the first substrate, including a second alignment key formed thereon, the second alignment key having at least third and fourth alignment marks, the third alignment mark being formed at a corresponding position of the first alignment mark of the first alignment key, the fourth alignment mark being offset at least a first predetermined distance in at least a first direction from the second alignment mark of the first alignment key. Using an alignment key of the present invention, since the upper and lower substrates can be correctly aligned each other, there is an advantage that a low yield resulting from an alignment error is prevented, and it is easy to identify a misalignment, quantify its magnitude in two directions, and thus be able to discern whether two substrates are correctly aligned with each other or not.