Introduction: This research was conducted to investigate the effects of Catharanthus roseus (Kemunting Cina), Kalanchoe laciniata (Setawar Kampung) and Piper longum (Kadok Kampung) on the in vitro proliferation of hormone dependent breast cancer (MCF-7) and colon cancer (Caco2) cell lines. Methodology:The effects of Catharanthus roseus, Kalanchoe laciniata and Piper longum extracts (hexane, chloroform, ethyl acetate and methanol extracts) on the cytotoxicity of MCF-7 and Caco2 cell lines were measured using (3-4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazoliumbromide) (MTT) assay. Results: Kalanchoe laciniata hexane extract showed significant inhibitions on MCF-7 carcinoma cell lines proliferation with IC50 value of 75.7 µg/ml. Catharanthus roseus extracts (hexane, chloroform and ethyl acetate) inhibited MCF-7 cells proliferation at concentrations of 80, 70 and 90 mg/ml, respectively. Discussion: IC50 value of all extracts of Piper longum and Kalanchoe laciniata chloroform, ethyl acetate and methanol extracts on the proliferation of MCF-7 cancer cells could not be determined, as it did not demonstrate any appreciable inhibition on the cellular proliferation at the concentration tested. However, Piper longum chloroform and ethyl acetate extracts showed anti-tumourigenic effect against colon cancer (Caco2) with IC50 of 87 mg/ml and 20 mg/ml, respectively. Kalanchoe laciniata hexane extracts inhibited Caco2 cellular proliferation with IC50 value of 100 mg/ml. Catharanthus roseus chloroform and ethyl acetate extracts inhibited Caco2 proliferation at IC50 of 28.2 µg/ml and 74.1 mg/ml, respectively. Conclusion: From this study, it can be concluded that only hexane extract of Kalanchoe laciniata was effective against cellular proliferations of MCF-7 while Piper longum was more effective in inhibiting Caco2 proliferations. However, both the herbs were not so effective against MCF-7 and Caco2 cell lines compared with Catharanthus roseus. Keywords: Catharanthus roseus, Kalanchoe laciniata, Piper longum, cytotoxicity