The content of extractive and acid-alkali property of Acacia mangium Willd woods were analyzed and their relationships were discussed.The result shows:(1)Acacia mangium Willd wood shows acidity and its pH is 5.34,the acid buffering capacity and alkali buffering capacity are 0.142 mmol and 0.053 mmol respectively,the extractive contents of cold-water,hot-water,1% NaOH and benzene-alcohol are 4.84%,5.75%,15.98% and 6.09% respectively.(2)the heartwood acid buffering capacities,the heartwood extractive contents of cold-water,hot-water,1% NaOH and benzene-alcohol are higher than sapwood,and decreased with the trunk height,the heartwood pH and alkali buffering capacity are lower than sapwood,and increased with the trunk height.(3)the pH shows negative correlation with the acid buffering capacity,the extractive contents of hot-water,1% NaOH and benzene-alcohol,and positive correlation with alkali buffering capacity and extractive content of cold-water.