We present sufficient conditions ensuring the lower and upper functions on the reversed-order for the periodic difference equations. This enables us to obtain the existence of positive periodic solutions of the second-order difference equation Δ 2 (−1) = ()/ ()− ℎ()/ () + (), ∈ Z, where , ℎ : Z → [0, ∞), and : Z → R are-periodic functions, , > 0.