Currently, there are many method of sewage water treatment. The coagulation with natural coagulant is safer and cheaper than chemical coagulant. This study is the experimental research design which aims to determine the appropriate pH value, the appropriate concentration of mangosteen peel extracts and the appropriate contact time for the effectiveness of sewage treatment with acetone mangosteen peel extracts.  The samples were collected from sewage water which passed through sand filter process of Saen Suk Municipality, Chonburi. The data were analyzed using descriptive statistics. The results found that mangosteen peel extract at pH 8 has the highest efficiency to treat turbid water as 62.15±31.22 percent and showed flocculation, apparently. A lower pH would inhibit flocculation. The appropriate amount of mangosteen peel extracts was 12 ml per liter (v/v) as 67.50±4.25 percent. A higher concentration, the removal efficiency of turbidity tends to decrease. The contact time at 60 minutes found that the turbidity removal efficiency of sewage water gradually increased as 95.45+6.23 percent. When increased contact time, the removal efficiency is closely with at 60 minutes.