The roadways that located around the beach are often have some problems with puddle of the seawater caused by the condition tides or known as rob water. Therefore, to find alternatife way due to prevent pavement damage, application of steel slag with higher quality is better to be used rather than ordinary aggregate. This research substitutes aggregate into the steel slag with 100% coarse aggregate number ½” and 50% fine aggregate number 30 that soaked in the seawater about 6 hours, 12 hours, and 24 hours. From this research, the longer this immersion is conducted will affect marshall characteristic resulting poor quality of asphalt, marked by decline of stability value, VFWA value, and also MQ value. As for the value of flow, VITM and VMA tend to rise. It can be concluded that asphalt soaked in the seawater resulting poor quality of asphalt.