In reliability optimization, two problems have been commonly considered by the researchers. These two problems are “Redundancy Allocation Problem (RAP)” and “Reliability-Redundancy Allocation Problem (RRAP)”. Traditionally in both RAP and RRAP problems, it is assumed that the redundant components are used based on predefined strategies. Generally, i reliability studies, two different strategie are considered to determine how the redundant component must be used. These strategies are called active and standby strategies. There are three variant of the standby redundancy called cold, warm, and hot standby which the cold strategy is more popular.In this thesis, anovel strategy that is a combination of traditional active and standby strategies is introduced. The newstrategy is called mixed strategy which uses both active and cold-standby strategies in one subsystemsimultaneously. Therefore, the problem is to determine the component type, redundancy level, number ofactive and cold-standby units for each subsystem in order to optimize the object function(s).As the optimization of RAP and RRAP belong to NP-hard justify; LINE-HEIGHT: normal; MARGIN: 0in 0in 0pt" To demonstrate the advantage of the new strategy and the proposed GA and NSGA-II algorithms, they areimplemented on some well-known test problems in the literature. Results demonstrate that the new strategy increases the reliability value of the all the benchmark problems considerably.This improvement can be very important for system designers, because thereliability of any system with the structure of redundant component ca be increased by changing the redundancy strategy, not by only adding redundant component. Moreover, this improvement dose not increases the cost, weight, volume or other known physical characteristics of the systems. Hence, it seems that the new strategy can take place the two previous strategies in scientific and application studies.