Hydroynamic fluid tortuosity is a parameter to describe the fluid streamlines average elongation. The motivation of the present study is introducing a new concept for theoretical predictions of dynamic tortuosity effects on mass transfer in a novel three-dimensional passive T-shape micro-mixer both experimentally and by numerical simulation. In the numerical analysis, continuity, motion, and diffusion-convection equations were solved, and the amount of mass transfer and the fluid tortuosity was calculated for different rectangular winglet angles. The Reynolds number is considered in the range of 0.1-93. The results show that when the angle of winglet tends to 22.5°, the fluid tortuosity, lateral velocity, and fluid mass transfer tend to maximum values. Furthermore, the effect of fluid tortuosity on the fluid stretching as a theory of chaotic mixing is investigated.