In this article fluid flow and conjugate conduction-convective heat transfer from a three-dimensional array of rectangular perforated fins with square windows that are arranged in lateral surface of fins are studied numerically. For investigation, Navier-Stokes equations and RNG based k - epsilon turbulent model are used. Finite volume procedure with SIMPLE algorithm is applied to coupled differential equations for both solid and gas phases. Computations are carried out for Reynolds numbers of 2000-5000 based on the fin thickness and Pr = 0.71. Numerical model is first validated with previous experimental studies and good agreement were observed. Based on a valid numerical model, numerical solution is made to find fluid flow and temperature distribution for various arrangements. For each type, fin efficiency of perforated fins is determined and compared with the equivalent solid fin. Results show that new perforated fins have higher total heat transfer and considerable weight reduction in comparison with solid fins. (C) 2008 Elsevier Ltd. All rights reserved.