Australian bush foods have been shown to have functional food and medicinal benefits but very few comprehensive scientific investigations have been undertaken on these plants. Two Australian fruits that have been highlighted as species warranting investigation are the berries of Tasmannia lanceolata (Tasmanian pepper berry) and Terminalia ferdinandiana (Kakadu plum). Both species have been used traditionally and are currently marketed as functional foods in addition to being exported overseas for various uses. The aim of this thesis was to investigate the antimicrobial bioactivity of the native fruits of T. lanceolata and T. ferdinandiana against a panel of pathogenic, food spoilage microbes, followed by a bioassay guided approach to isolate the bioactive molecules within the active extracts. Both fruits possess antimicrobial activity with low toxicity and preliminary phytochemical screening indicated that the fruits contain a suite of chemical classes including phenols, flavonoids, terpenes and saponins. The methanol extract was the most potent antimicrobial extract from T. ferdinandiana fruit, while the ethyl acetate extract was the most potent antimicrobial extract from the berries of T. lanceolata. HPLC separation of these selected bioextracts was followed by antimicrobial bioactivity testing and finally compound structural characterization using spectroscopic methods such as electrospray mass spectrometry and 1D (1H and 13C) and 2D (COSY, HSQC, HMBC and ROESY) NMR spectroscopy. This resulted in seven small tannins, corilagin, 1,3,6-trigalloyl glucose, elaeocarpusin, geraniin, chebulagic acid, helioscopin B and chebulinic acid being identified as the antimicrobial active molecules from T. ferdinandiana fruit.