High water-content flowable fill often utilized as a back-fill material for foundations, buried pipes, etc. in urban areas, is investigated with a special emphasis on cyclic loading effect due to strong earthquakes. As a basic step of the research, only kaolinite clay is used for slurried soil mixed with cement, yielding the following major findings. The soil keeps its original undrained strength even after cyclic loading with high stress amplitude, but deformation modulus tends to decrease with the increase of cyclic loading amplitude. Consolidation yield stress which is dependent on the cement content and slurry density has a great effect on its mechanical properties.