Many offshore airports are constructed by reclamation and some expanded runways of near shore airports are extended from reclaimed land to the sea in Japan. On such airports, an approach light system is installed in the sea and a long jetty supported in vertical piles is required for inspection of many lights of the system. The estimation of wave uplift force become important because of low clearance of jetty face above sea level. The uplift pressure by sea wave, however, has not been enough understood yet except of standing wave in front of a piled wharf. In this study, model experiment is conducted to estimate the uplift wave pressure acting on a long thin piled jetty with the condition of waves.
　According to the results of these model experiments, it is confirmed that the maximum uplift pressure is appeared at X/L=0.5, that is the nearest wave standing point as X is the distance from the seawall covered with armor blocks and L is the incident wave length. The traditional design formula; pk=4gH proposed by Ito and Takeda (1967) can be still applied in X/L≤0.5. On the other hand, it is cleared that the design uplift pressure under the offshore part of piled jetty can be reduced according to the relative clearance for the acting wave height in each position, and new design formulae are newly proposed in X/L>0.5. Moreover, the probability density of the appearance of uplift pressure is estimated for random waves.