A new micromixer design based on uniform circular obstacles and cross flow (UCCFM) of the fluid streams was proposed. Water-ethanol and oil-ethanol mixing was assessed for Reynolds numbers ranging from 0.1 to 100 by CFD simulations. The performance index was evaluated providing the ratio of fluid mixing degree (MI) to the unit of pressure drop along the micromixer. For both systems, the highest performance indexes were noticed at Re = 0.01, a flow regime characterized by molecular diffusion controlling the mass transfer. The UCCFM design with diameter = 600 µm allowed good fluid mixing for water-ethanol at Re = 0.01 (MI = 0.815) with a very low pressure drop of 0.123 Pa. For oil-ethanol mixing, the MI = 0.693 was obtained with a pressure drop of 76.06 Pa. The UCCFM presented a superior MI in low Reynolds number regarding other micromixer designs in literature.