Abstract: A frame assembly structure includes two lateral panels, a corner post, and a positioning element. The positioning element has an elongate body portion. A. shoulder portion extends from each of two ends of the body portion. An included angle is formed between the shoulder portion and the body portion. The shoulder portion has two hanger holes each having a round hole expanding to form a recess. The body portion has two through holes centrally. Hanger nails are disposed at each lateral panel, and correspond in position to the hanger holes. Heads of the hanger nails penetrate the round holes such that the recesses receive bodies of the hanger nails engageably, allowing two adjacent lateral panels to be connected at right angle. The corner post is engaged with the two adjacent lateral panels and engaged with the positioning element by passing fastening elements through the through holes.