This research investigates the effect of the post-cure time on the residual stresses in laminated composites. Laminated composites were made of T300 carbon fibers and epoxy resin. The post-cure process was carried out at the constant temperature of 120 °C for 6 and 12 hours for two specimens. The slitting method was employed to determine through-thickness residual stress distribution of the composite laminates. The experiment results show that the increasing the post-cure time lead to the reduction of maximum residual stress as well as the uniformity of the residual stress distribution in laminated composites. Therefore, increasing the post-cure time is an effective way of reducing the destructive effects of residual stresses in laminated composites.