Abstract : Medicinal plant was wildly used at recent year for treated many diseases instead of chemical drugs because of less in side effect. Cassia angustifolia leaves extract was investigated in this study as anti-proliferation agent for type of breast cancer cell. C.angustifolia (CA) ethanol leaves extract and its fractions (CAF) were evaluated in vitro for the MCF7 cell line and MDA-MB-231 cell line as anti-proliferation. The cells were treated in different doses for CA and CAF at 24h and 28h. The treated cells were stained with AO/EB stain to evaluated apoptosis effect of CAF. GCMS method was used to identify active component in the CAF that give highest anti-proliferation activity. Leaves extract of C.angustifolia was identified as anti-proliferation for MCF7 cell line and MDA-MB-231 cell line. The result was revealed that CAF1 was had highest inhibition percentage for both cells, in (76.73 ± 0.23) % for MCF7 cell and (70.49 ±2.6) % for MDA-MB-231cell. Apoptosis percent present for treated MCF7 cell at 24h and 48h was (84.32 ±22.42) and (72.32 ± 25.08) respectively. And for treated MDA-MB-231cell was (60.16 ± 40.13), (65.31 ± 30.28) respectively for the highest dose 1000 µg/mL. GCMS analysis was identified 23 active component as 2-Pentanone, 4-hydroxy-4-methyl- and 2H-Pyran, 2-(2-heptadecynyloxy), Hexadecanoic acid, methyl ester, Oxalic acid, Phthalic acid, di(2-propylpenty, 2-Pentadecanone, 6,10,14-trimet,and Carbonic acid, decyl tridecyl ester, 2-Tetradecynal, 4-hydroxy-, Tritriacontane, Tricosane, Hexadecanoic acid, methyl ester and Hexadecanoic acid, ethyl ester, Pentadecanoic acid, 14-methyl ester, Heptadecanoic acid, 16-methyl- , Methyl 8-oxooctanoate, Hexadecyl propyl ether, Undecanal, Octadecanoic acid, ethyl ester, 3-Methyl-4-(phenylthio)-2-prop-, dimer of Coleon F. In conclusion that C.angustifolia frication1 for ethanol leaves extract has anti proliferation and antitumor effect on the breast cancer by enhanced apoptosis pathway that lead to programmed cell death for cancer cell and prevent metastasis of its. For that CAF1 could be as new drug to treat aggressive breast cancer.