Abstract: The invention discloses a method for treating a heavy metal containing waste water by using acorns. Acorns and nuts of other trees belonging to the Eagaceae group are dried at the room temperature and under the sun beams. Then acornic acid is extracted from the dried acorns. Then the acornic acid is filtered until it becomes colorless. A heavy metal containing waste water (low concentration and high concentration) is maintained at pH=8-11.5 by adding NH.sub.4 OH, Ca(OH).sub.2 and NAOH. Then the acornic acid is added into the waste water, and then, Ca.sup.++ ions singly or together with other divalent cations are added by 50 ppm. Then this solution is agitated for several minutes, and then, the heavy metals are precipitated, or the solution is filtered, thereby treating the heavy metal containing waste water.