This work aimed to obtain and investigate the properties and composition of extracts from flowers of Acacia mearnsii; this tree is widely cultivated because the bark is used as a raw material for various industry segments, but the flowers are not yet explored. The essential oil was evaluated by GC/FID, GC/MS, and GC/O. The antioxidant activity (DPPH and phosphomolybdenum methods) and chemical composition were investigated for a water-soluble extract, a by-product of the extraction process. 85.8% of the compounds present in the essential oil were identified, 8-heptadecene being the major compound. The main scents detected by the olfactory analysis were roast nutty, coffee, sweet, and floral. The water-soluble extract showed antioxidant activity that may be related to phenolic compounds. Results obtained from the LC-qTOF/MS analysis have shown that 25 likely flavonoids, such as naringenin, myricetin, quercetin, and rutin are present in the extract.