Three-dimensional shaking table tests were carried out for a new base-isolation system of a lightweight building with a mat foundation. The new system uses resin balls between the mat and an under-mat reinforced concrete slab. A type using fiber-reinforced cement boards and phenol resin balls caused a load concentration in its virgin state and amplified its response in case of a small input. Another type with layers of polystyrene foam, the cement board, polystyrene balls and the cement board absorbed relative unevenness between the moving mat and the under-mat slab and decreased its acceleration under about 40 cm/sec^2.
