Callistemon citrinus is a member of Myrtaceae family that thrives under different ecological conditions. The leaves, flowers, stem backs and roots of the plant contain various phytochemicals that are useful in folk medicine for different remedies such as antimicrobial, anti-nociceptive, fungicide and anti-inflammatory purposes. In this study, we investigated the cytotoxic effect of Callistemon citrinus leaf and flower methanolic extracts against human Colo-205 Cell Line using real time cell analyzer device for monitoring in time-dependent manner. To determine the mechanism of cytotoxicity of the extracts, Western blotting assay was used for measuring evocation of Akt pathway. Extracts were found to exert cytotoxic effect at a dose dependent manner. IC50, values of leaves and flowers extract were 6.49 mu g/mL and 5.22 mu g/mL, respectively. At the early stages of the experiment, Akt pathway was triggered at high extract concentrations. Although, high extract concentrations showed proliferative effect at early stages, this effect reversed after 5 and 8 h resulting in low cell viability. Findings from this study therefore showed that extracts of leaf and flower from Callistemon citrinus demonstrated cytotoxic effect against Colo-205 but seems not to be related Akt signaling pathway.