A previously undescribed phenolic sulphate ester, potassium 34-dihydroxy-3-methoxybenzoic acid methyl ester-5-sulphate (1), along with nine known flavonoids, kaempferol-3-O-potassium sulphate-4′,7-dimethyl ether (2), kaempferol-4′,7-dimethyl ether (3), rhamnocitrin-3-O-potassium sulphate (4), rhamnocitrin (5), kaempferol (6), quercetin (7), afzelin (8), quercetin-3-O-α-l-rhamnopyranoside (9) and luteolin-3′-O-potassium sulphate (10) were isolated from the aerial parts of Tamarix balansae. Structures elucidation was performed by comprehensive 1D and 2D NMR analyses, mass spectrometry and by comparison with literature data. The antibacterial assay against Enterococcus faecalis, Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli and Pseudomonas aeruginosa bacteria showed a good activity for 2, 3, 7 and 9, with MICs ranging from 62.5 to 250 μg/mL. The abilities of these compounds to scavenge the DPPH were evaluated. Compounds 1, 7, 9 and 10 exhibited a good antiradical activity potential with IC50 values ranging from 3.0 to 115.5 μg/mL, compared with ascorbic acid (IC50 7.4 μg/mL) which was used as positive control.