This work investigated the effect of leaf development (maturity) on morphology, antimicrobial activity, total phenolic (TPC) and ascorbic acid content in leaves of Terminalia ferdinandiana, an endemic plant of Australia. The results of this study indicated that total ascorbic acid was in the range of 23.0 to 35.5 mg/100 g dry weight (DW), showing an increase with advance of maturity. TPCin water and methanolic extracts were in the range of 237.3-598.6 and 210.3-319.6 mg Gallic acid equivalent (GAE)/ g DW, respectively. Leaf extracts exhibited pronounced inhibitory activity towards Staphylococcus aureus where total ascorbic acid and TPC were positively correlated with the observed antimicrobial activity. These results indicated that leaves extracts might be used asan alternative to synthetic antimicrobial agents, with a great potential for application as an environmentally friendly sanitizer in the hospitality and healthcare industries.