[Angka kejadian penyakit mieloma multipel kecil, yaitu 0,8% di dunia dan 0,6% diAsia Tenggara dari seluruh kasus kanker yang ada. Namun, penyakit ini terjadisecara asimtomatik sehingga sulit didiagnosis, belum dapat disembuhkan, danmudah mempengaruhi organ dalam tubuh. Kulit buah manggis yang jarangdimanfaatkan diketahui mengandung senyawa xanton (polifenolat) yang memilikiaktivitas antikanker. Penelitian in vitro menggunakan sel jalur p3x63ag8 untukmenemukan ada tidaknya efek sitotoksisitas ekstrak etanol kulit buah manggis sertaIC50. Sel dibagi menjadi 9 kelompok, yaitu 1 kelompok kontrol dan 8 kelompokperlakuan dengan konsentrasi 6,25 μg/ml, 12,5 μg/ml, 25 μg/ml, 50 μg/ml, 100μg/ml, 200 μg/ml, 400 μg/ml, dan 800 μg/ml. Data diambil dengan metode MTTassay dan hasilnya berupa nilai optical density. Setelah inkubasi 48 jammenggunakan ekstrak etanol kulit buah manggis, hasil persamaan garis diketahuiIC50 nya adalah 5,41 μg/ml. Analisis statistik dengan Kruskal Wallis menghasilkanadanya perbedaan efek sitotoksik pada konsentrasi yang berbeda . Uji Post Hocdidapatkan perbedaan bermakna antara kelompok kontrol dan kelompok perlakuan6,25 μg/ml dengan kelompok perlakuan lain.;Multiple myeloma disease has small incidence, namely 0,8% in the world and 0,6%in Southeast Asia of all cancer cases. However, the diasease occurs in asymptomaticthat so difficult to be diagnosed, can not be cured, and affects many organs. Themangosteen pericarp which rarely used evidently contain xanthone (polifenolat)compound which have anticancer activity. Research in in vitro manner using celllines p3x63ag8 to discover the presence of cytotoxicity effect of mangosteenpericarp ethanol extract and the IC50. Cells was divided into 9 groups, 1 controlgroup and 8 treatment groups (consentrations: 6,25 μg/ml, 12,5 μg/ml, 25 μg/ml,50 μg/ml, 100 μg/ml, 200 μg/ml, 400 μg/ml, and 800 μg/ml). Data taken by MTTassay method and the result is optical density value. After 48-hours incubationperiod and the result in line equation, found that IC50 was 5.41 ug / ml. Statisticalanalysis with Kruskal Wallis declared differences in the cytotoxic effects ofdifferent concentrations.Post Hoc test found significant difference beetwen thecontrol group and the treatment group of 6.25 ug / ml just than other groups;Multiple myeloma disease has small incidence, namely 0,8% in the world and 0,6%in Southeast Asia of all cancer cases. However, the diasease occurs in asymptomaticthat so difficult to be diagnosed, can not be cured, and affects many organs. Themangosteen pericarp which rarely used evidently contain xanthone (polifenolat)compound which have anticancer activity. Research in in vitro manner using celllines p3x63ag8 to discover the presence of cytotoxicity effect of mangosteenpericarp ethanol extract and the IC50. Cells was divided into 9 groups, 1 controlgroup and 8 treatment groups (consentrations: 6,25 μg/ml, 12,5 μg/ml, 25 μg/ml,50 μg/ml, 100 μg/ml, 200 μg/ml, 400 μg/ml, and 800 μg/ml). Data taken by MTTassay method and the result is optical density value. After 48-hours incubationperiod and the result in line equation, found that IC50 was 5.41 ug / ml. Statisticalanalysis with Kruskal Wallis declared differences in the cytotoxic effects ofdifferent concentrations.Post Hoc test found significant difference beetwen thecontrol group and the treatment group of 6.25 ug / ml just than other groups, Multiple myeloma disease has small incidence, namely 0,8% in the world and 0,6%in Southeast Asia of all cancer cases. However, the diasease occurs in asymptomaticthat so difficult to be diagnosed, can not be cured, and affects many organs. Themangosteen pericarp which rarely used evidently contain xanthone (polifenolat)compound which have anticancer activity. Research in in vitro manner using celllines p3x63ag8 to discover the presence of cytotoxicity effect of mangosteenpericarp ethanol extract and the IC50. Cells was divided into 9 groups, 1 controlgroup and 8 treatment groups (consentrations: 6,25 μg/ml, 12,5 μg/ml, 25 μg/ml,50 μg/ml, 100 μg/ml, 200 μg/ml, 400 μg/ml, and 800 μg/ml). Data taken by MTTassay method and the result is optical density value. After 48-hours incubationperiod and the result in line equation, found that IC50 was 5.41 ug / ml. Statisticalanalysis with Kruskal Wallis declared differences in the cytotoxic effects ofdifferent concentrations.Post Hoc test found significant difference beetwen thecontrol group and the treatment group of 6.25 ug / ml just than other groups]