A new cyclic 4-hydroxy-dithiosulfonate, bruguiesulfurol (1), as well as two known 4-hydroxydithiolane 1-oxides, brugierol (2) and isobrugierol (3) were isolated from the flowers of Bruguiera gymnorrhiza. With stably-transfected HepG2 cells, the three isolates activated antioxidant response element (ARE) luciferase activation with (EC50) values of 56.7, 3.7 and 1.8 μM, respectively. Compounds 2 and 3 also inhibited phorbol ester-induced NF-κB (nuclear factor-κB) luciferase activity with IC50 values of 85.0 and 14.5 μM, respectively. In addition, compound 2 inhibited enzyme cyclooxygenase-2 (COX-2) activity with an IC50 value of 6.1 μM. The structures of these isolates were determined by spectral data, and that of compound 1 was confirmed by X-ray crystallographic analysis.