In this research, the effect of the gravel contents on the liquefaction behavior of the isotropically consolidated gravel-sand specimen is investigated. For these purpose, the cyclic triaxial tests for isotropically consolidated specimens are performed at the same relative density(Dr=40%) and void ratio(e=0.7) with various gravel contents. Test results show that, for the isotropically consolidated specimen at the 40% of relative density with low gravel contents pore water pressure development and axial strain behavior represent the similar behavior to the loose sand mainly due to high void ratio, but, for the specimens with high gravel content(70%), both behaviors tend to be similar to the dense sand. And the liquefaction strength increases with increasing GC. On the other hand, the same void ratio(e=0.7) with higher gravel contents show the same behaviors of pore water pressure development and axial strain as the loose sand behaviors due to lower relative density, but, for the lower gravel content, these behaviors show the representative behavior of the dense sand. And the strength increases with decreasing GC. Thus, it is confirmed that the liquefaction strength of the gravel-sand soils depends both on relative density and void ratio of the whole mixture rather than the relative density of the sand matrix.