Abstarct: In this thesis, the formation of microbubbles inside venturi tube is studied via numerical and experimental methods. Micro-nano bubble is one of the newest technologies in the field of nano-fluidics. Its applications include flotation of particles in the liquid, water and wastewater treatment, drag reduction, medicine and health, aquaculture and agriculture, especially hydroponic cultivation. In this research, various samples of venturi tubes were analyzed by OpenFOAM software and by studying microbubble formation, appropriate samples were selected for designation of experimental models. For numerical analysis, the standard κ _ε method has been used. Experimental models were prepared and following injection of air and water flow into Venturi tube, the images and films of the two-phase flow inside Venturi tube were recorded by a high-speed camera (4500 frxames per second). The prepared images and films were processed by Image processing technique and programming in MATLAB software. The border between micro and macro bubbles diameter is considered 1000 micrometers. The results suggest that flow regimes inside venturi tube are similar to flow regimes inside horizontal tubes, and for having bubbly flow and consequently formation of microbubbles, air phase flow rate must be very smaller than water phase. By changing venturi tube’s dimensions, it was observed that least pressure drop takes place in the junction of the contraction section to the throat section. It was also observed that decreasing the slope of diffusion and contraction sections increases pressure drop and as the slope of contraction and diffusion sections is equal (>24 degrees), better results are achieved regarding microbubbles formation. Experimental results show that by decreasing throat section’s length and by increasing flow rate, more micro-nano bubbles form. the maximum bubble diameter is related to the Sauter diameter with coefficient of proportionality 1.673.