This study is to experimentally investigate the heat transfer enhancement by perforation in air cooling of two in-line rectangular heat sources module. Two separation distances between the heat sources were investigated at s/L = 0.5 and 1.0. The area between the heat sources in both cases were perforated in aligned arrangement such that the holes open area ratio (b) are of 0, 0.0736, 0.1472 and 0.2944. The dimensionless temperature distribution and the average Nusselt number are considered at different values of Reynolds number (3391 6 ReL 6 10798) and holes open area ratio. It could be seen that perforation could enhance the heat transfer coefficients and reduce the module temperature significantly. Correlations are obtained for the average Nusselt number utilizing the present measurements within the investigated range of the different parameters.