Flow structure and heat transfer characteristics around two-equal in-tandem square cylinders in the two dimensional laminar and turbulent flow regimes are simulated numerically for Reynolds and Prandtl numbers, Re=1-1×105, Pr=0.71, respectively. The investigation is based on an implicit finite volume scheme for integrating the unsteady Navier-Stokes equations and use of standard κ-ε model to Reynolds stresses and scalar fluxes terms modelling. In this study, the instantaneous and mean streamlines, vorticity and isotherm patterns for different Reynolds numbers and distance between the cylinders are presented and discussed. In addition, the global quantities such as drag coefficients, RMS lift and drag coefficients, Strouhal number and Nusselt number are determined. An interesting phenomenon has been observed in the flow patterns depending upon the Reynolds number and the distance between the cylinders. A switch over in the nature of the fluctuations of the lift and drag coefficients has been also observed with the increase of Reynolds number and the distance between the cylinders. The numerical results are in good agreement with the experimental and numerical data available in the literature