The aerodynamic characteristics and the effects of tip plates of a tapered supersonic biplane wing during the starting process were investigated by experimental and computational fluid dynamics (EFD/CFD). Three types of wing models were used: one with a tip plate covering only the aft-half of the wing tip (type-A); one with a tip plate covering the entire wing tip (type-B); and one without a tip plate (type-N). Experiments were conducted in a supersonic blowdown wind tunnel 600 × 600 mm in cross-section located at the high-speed wind tunnel facility of the Institute of Space and Astronautical Science (ISAS/JAXA). The flow conditions ranged from M_∞ = 1.5 to 1.9 in increments of 0.1. Pressure-sensitive paint was applied to measure the pressure distributions on the wing surface. CFD simulations were conducted for comparison with the experimental results and for detailed investigation of the effects of the Mach number. The tapered biplane wing without a tip plate is found to start between M_∞ = 1.8 and 1.9. The difference in starting Mach number between type-N and type-A is small. On the other hand, the starting Mach number of type-B is approximately 0.05 higher than that of type-N.