This paper designs an optimal controleer for thickness-tension control in hot strip finishing mills. A state space model considering the interaction characteristics between thickness and tension is derived, where looper dynamics are not considered. Next, a thickness-tension optimal controller is designed using an ILQ(Inverse Linear Quadratic optimal control) algorithm, and it is combined with a feedforward controller based on a minimal disturbance observer. Finally, it is shown from a computer simulation that the proposed optimal controller is very effective in thickness-tension control under some disturbances, in particular it can consider the interaction dynamics between thickness and tension.