An experiment to investigate the effect of pseudo-shock wave (PSW) on turbulent diffusion of a transverse jet in a Mach 2.0 supersonic crossflow was conducted. The vertical jet from a 2.5 mm-diameter orifice was injected into pseudo-shock wave and jetto-crossflow momentum flux ratio was 2.2. To measure turbulent diffusion flux, stereoscopic particle image velocimetry (SPIV) and acetone planar laser-induced fluorescence (PLIF) system were combined and velocity and concentration fields were simultaneously measured. Measurement plane was a cross section at 10 mm downstream from the injection port. The position of PSW was controlled by a flow plug at the duct exit driven by a stepping motor. The front of PSW was set at 30 mm upstream from the orifice. Without PSW, turbulent diffusion flux (TDF) of the injectant was extended upward and the shape of injectant plume was deformed by a counter-rotating vortex pair (CVP) which was formed behind the injected gas. Under PSW, the CVP made horseshoe-shape concentration distribution. TDF directed from spur of concentration to both free stream side and lee side of the jet. Most of no-PSW condition and outward of under-PSW TDF was concentration-fluctuation-dominant, only inward TDF under PSW emerged as turbulent-dominant. The effect of PSW that enhances diffusion of injected gas was confirmed.