The increasing need to investigate high-speed accelerating and decelerating flows led to the development of the symmetric sliding-block variable Mach number wind tunnel. This intermittent, blow-down, enclosed free-jet type wind tunnel can generate variable Mach numbers during the wind tunnel operation. The variable Mach number flow is achieved by changing the area ratio by translating nozzle blocks symmetrically. A single lead screw is used for the translation of nozzle blocks. The details of the design and characterization of this wind tunnel are presented. The wind tunnel nozzle is calibrated with a pitot rake for different translations. The variable Mach number flow is characterized by pressure measurements at a high sampling rate and high-speed Schlieren images. The Mach numbers obtained with these two methods match well with each other. The Mach number range of this wind tunnel is from 2 to 2.72. The wind tunnel can generate both acceleration and deceleration of the flow depending on the translation direction. The uniform test section area of the wind tunnel is 40 mm in width by 20 mm in height. The Mach number variation is less than 1.4 % in the uniform test area. The absolute dM/dt of the wind tunnel is 3.75, whereas the local dM/dt is higher. The symmetric sliding-block type can generate high acceleration and deceleration rates, simulating actual flight conditions.