An outdoor experiment was set up to investigate the effects of used lubricating oil (5 L/m2) on Aegiceras ciculatum Blanco. and Avicennia marina (Forsk) Vierh., two salt-excreting mangroves. A. marina was more sensitive to used lubricating oil than A. ciculatum and canopy-oiling resulted in more direct physical damage and stronger lethal effects than base-oiling. When treated with canopy-oiling, half of A. ciculatum plants survived for the whole treatment time (90 d); but, for A. marina, high mortality (83%) resulted from canopy-oiling within 3 weeks and no plants survived for 80 d. Base-oiling had no lethal effects on A. ciculatum plants even at the termination of this experiment, but 83% of A. marina plants died 80 d after treatment. Forty days after canopy-oiling, 93% of A. ciculatum leaves fell and no live leaves remained on A. marina plants. By the end of the experiment, base-oiling treatment resulted in about 45% of A. ciculatum leaves falling, while all A. marina leaves and buds were bed to die. Lubricating oil resulted in physiological damage to A. ciculatum leaves, including decreases in chlorophyll and carotenoid contents, nitrate reductase, peroxidase and superoxide dismutase activities, and increases in malonaldehyde contents. For both species, oil pollution significantly reduced leaf, root, and total biomass, but did not significantly affect stem biomass. Oil pollution resulted in damage to the xylem vessels of fine roots but not to those of mediate roots.