H.264/AVC is the latest video coding standard from ITU-T. It provides superior and efficient video coding at low bit rates. Flexible macroblocks ordering (FMO) is an error-resilient tool included in H.264/AVC. In this paper, a novel technique for adaptive classification of macroblocks into two slice groups using FMO method is proposed. With our adaptive macroblocks allocation map, simulation results have shown the improved FMO works better with the error concealment tool in H.264/AVC. Simulations also show that our approach performs nearly as well as the chess-board pattern but has better coding efficiency.