Cancer is referred to as uncontrolled abnormal proliferation of body cells. Currently cancer treatment and management is a challenge due to complexity of the disease, toxicity of chemotherapy, unaffordability of treatment and severe side effects. Therefore, it is imperative to investigate complementary and alternative medicine for leads and development of anticancer drugs. Cassia abbreviate (C. abbreviata) has been traditionally used for its ethnotherapeutic properties and pharmacological activities. It has been reported to possess antiproliferative activity, though there is no scientific evidence to validate this claim. The main objective of this study was to determine the antiproliferative activity of aqueous root bark extract of C. abbreviata on hepatocellular carcinoma (HCC), vero, and macrophage cell lines in vitro. The antiproliferative activity of aqueous root bark extract of C. abbreviata was determined using MTT assay. The results showed that aqueous root bark extract of C. abbreviata has antiproliferative activity against HCC, vero and macrophage cell lines. The extract had the highest antiproliferative activity against HCC cell line with an IC 50 of 1.49 µg/ml as compared to 81.08 µg/ml and 128.38 µg/ml in macrophages and vero cells respectively. The IC 50 observed on non-cancerous normal cells (macrophages and vero cells) indicated that the plant extract had little antiproliferative effects on normal cells hence regarded as safe. The extract contained flavonoids, phenols, tannins and saponins. In conclusion the antiproliferative activity of aqueous root bark extract of Cassia abbreviata observed could be attributed to the phytochemicals present in this plant extract. The results of this study, validates the claim that aqueous root bark extract of C. abbreviata has antiproliferative activity and justifies its use in herbal medicine.