A heat treatment apparatus for manufacturing a liquid crystal display panel through an in-situ process includes a body and a hardening unit, an annealing unit, and a transferring unit disposed on the body. The hardening unit heats a sealing member within a liquid crystal display panel to harden the sealing member. The annealing unit anneals liquid crystal within the liquid crystal display panel sealed by the sealing member. The transferring unit transfers the liquid crystal display panel between the hardening unit and the annealing unit. Therefore, the sealing member may be hardened and the liquid crystal may be sealed through an in-situ process to enhance productivity.