The entropy generation has been numerically investigated in concentric curved annular square ducts under constant wall temperature boundary condition. The problem has been assumed to be steady, hydrodynamically and thermally fully developed and incompressible laminar flow with constant physical properties. The solutions of discretized equations for continuity, momentum and energy have been obtained by using an elliptic Fortran Program based on the SIMPLE algorithm. Solutions have been achieved for i) Dean numbers ranging from 3.6 to 207.1, ii) Annulus dimension ratios of 5.5, 3.8, 2.9 and 2.36, and iii) Prandtl number of 0.7. in this regard, local entropy generation as well as overall entropy generation in the whole flow field has been analyzed in detail. Moreover, the effects of Dean number and annulus dimension ratio on entropy generation arising from the friction and heat transfer have been investigated. Accordingly, it is concluded that the effect of volumetric entropy generation that is a result of fluid frictional irreversibility can be neglected as compared with volumetric entropy generation due to heat transfer irreversibility. As Dean number increases, the distribution of volumetric entropy generation coming out from the heat transfer irreversibility is formed by the temperature field, which is depending on the curvature.