The aerodynamic characteristics and the effects of tip plates of a tapered supersonic biplane wing during the starting process have been investigated through Experimental and Computational Fluid Dynamics (EFD/CFD). Three types of the wing model were used: without tip plate (type-N); with the tip plate which covers only the aft-half of the wing tip (type-A); with the tip plate which covers the entire wing tip (type-B). Experiment was conducted in the supersonic blowdown wind tunnel with 600 mm × 600 mm cross section located at the High-speed Wind Tunnel Facility of Institute of Space and Astronautical Science (ISAS/JAXA). The flow conditions covered from M∞ = 1.5 to 1.9 with increments of 0.1. Pressure-Sensitive Paint was applied to measure pressure distributions on the surface of the wing. CFD simulations were conducted to compare with experiments and to investigate effects of the Mach numbers in detail. The tapered biplane wing without the tip plate was found to start between M∞ =1.8 and 1.9. The difference of the starting Mach numbers between type-N and type-A was small. On the other hand, the starting Mach number of type-B was about 0.05 higher than that of type-N.