We present a miniaturized microbubble generator via three-dimensional (3D) printing for potential use in gas-liquid chemical reactions. We design it based on venturi channel structures to enable continuous gas dispersion by turbulent interactions and fabricate it using 3D printing for its high design flexibility and fast manufacturing speed. By experiments using water and nitrogen, we discuss quantitatively the dependence of the formed microbubble characteristics on operating conditions and geometric parameters. In particular, predictive models of Sauter mean diameter of daughter bubbles are proposed to help select proper operating and design parameters in order to achieve the desired level of microbubbles. To further improve the performance, we explore series- and parallel-venturi configurations and find that the parallel-based assembly performs significantly better. Therefore, we prove that the 3D printed venturi microbubble generator has high potential for the flow chemistry community to implement gas-liquid reactions.