The cytotoxic effect of a hexane extract of Cassia alata (C alata) leaves in parental and Caspase 8, 3 and 9 negative A549 lung cancer cells was evaluated after a 24-hour treatment period. C alata extract was cytotoxic in parental and caspase-9 negative, but not caspase 3 and 8 negative A549 cells. The IC50 values were 143 μg/ml and 145 μg/ml in parental and caspase 9 negative A549 cells respectively. The flavanoid kaempferol was identified as a constituent of C alata leaf extract. These results suggest a cytotoxic effect of C alata that is dependent on caspase 8.