A large soil confinement box (LSCB) has been designed and constructed for seismic performance testing of large-scale geo-structures on the large high performance outdoor shake table (LHPOST) at the University of California–San Diego (UCSD). The LSCB is a rigid rectangular box with an open roof that covers the footprint of the LHPOST and has interior dimensions of 10.1 m (length) by 7.6 m (height) by 4.6 m or 5.8 m (width), depending upon assembly configuration. Boundary treatments are used to reduce side friction on the longitudinal walls and prevent slippage at the base. Shaking tests conducted on the empty LSCB indicate first resonance at 22–23 Hz, which is above the normal operating frequency of the LHPOST and should not significantly affect the measured dynamic response of geo-structure specimens. Tests conducted for a mechanically stabilized earth (MSE) retaining wall and two rocking bridge foundations indicate the versatility of the LSCB, including the capability to incorporate a liner and add water for tests on foundation soils with a shallow phreatic surface.