A field monitoring was conducted to examine the wind-attenuation effect of mangrove plantations at the Sanjiang Bay of Dongzhai Harbor, Hainan Province of South China. The wind speed and wind direction were measured at a site 50 m away from the offshore forest fringes of Sonneratia apetala and Kandelia obovata plantations and 2 m above the ground. Both the S. apetala and the K. obovata plantations had obvious effect in attenuating the speed of the wind from northerly to the shore, with the mean wind speed decreased by > 85% and the better effect of K. obovata plantation. With the increase of the wind speed, the wind-attenuation effect of the plantations presented a trend of decreasing first and remained stable then. At 50 m away from the offshore forest fringe of S. apetala plantation, the wind-attenuation rate was higher than 89.8% when the mean wind speed was lower than 5 m x s(-1), tended to be stable when the mean wind speed was 10 m x s(-1), and turned to be 58.9%-63.6% when the mean wind speed was higher than 15 m x s(-1). The S. apetala plantation had better wind attenuation effect in warmer season than in colder season. Under the extremely adverse weather like typhoon, the mean wind speed and extreme wind speed at 50 m away from the offshore forest fringe of S. apetala plantation were decreased by 59.4% and 53.2%, respectively.