We have experienced frequent failure of shear wave elastography (SWE) on kidney. In our past investigation, the shear wave (SW) arrival was unclear, or could not be distinguished from the background fluctuation in the displacement profile. In this study, we investigated the physical mechanism of this phenomenon in detail. Here we made three hypotheses: (1) Generated SW is obscured because of blood flow, (2) Push-pulse cannot generate SW in kidney, (3) Complicated structure with dense and fine renal vessels interferes with the propagation of SW. We analyzed received IQ data of SWE for three excised swine kidneys, a natural sponge (to mimic porous structure of the kidney), and two healthy volunteers (liver and kidney). The swine kidneys and the sponge were scanned in water. The ultrasound scanner used was LOGIQ E9 (GE Healthcare) with a 3.5 MHz convex probe (C1-6-D). For the volunteer scan, acoustic intensity of the push-pulse was varied between three levels: same level as clinical recommendation, a half of it, and zero (no push). When scanning livers, we included a large portal vein intentionally for comparison. Acquired IQ data (echo signals of a series of tracking pulses) were transferred into a PC and analyzed into the velocity distribution and its change over time after push-pulse insonification. Those changes of velocity distribution were visually inspected, while average velocity and standard deviation were calculated over time inside the area of push-pulse insonification. For the swine kidney, SWE images were sufficiently homogeneous. IQ data analysis revealed an evident propagation of SW. For the volunteer, typical velocity peak was observed in liver and kidney. Amplitudes of SW were sufficient compared to the background fluctuation by blood flow, and this fluctuation was larger in kidney than in liver. At the same time, however, kidney contained many pixels which indicate irregular velocity profiles. In those pixels, background velocity fluctuation was large, and therefore a typical pattern of shear wave arrival was not recognized. Such signals were also observed in a large portal vein. In addition, the shape of generated SW was different between the two organs, especially in one of the two volunteers. The region of excitation (area of deformation induced by push-pulse) was wide and not smooth in kidney. The sponge also presented such a rough velocity distribution, while the average velocity induced by the push-pulse was comparable with that for livers and kidneys. The background fluctuation in velocity profile decreased with higher push-pulse intensity level in both liver and kidney. This implies that the shear wave has an effect of pushing blood flow out from its traveling area. From all the above results, we concluded that all the three hypotheses were reasonable. As for the second hypothesis, based on the sponge experiment results, it is suggested that it is rather inhomogeneous and porous structure than vascularity that affects the appearance of generated shear wave. Considering the result of swine kidney, however, the vascularity is thought to contribute to the characteristic structure of kidney. The question remains why the clear SW generation was observed in one volunteer’s kidney (and why not in the other’s). The difference in speed and pressure of the blood flow might be one of the possible factors.