The addition of reclaimed asphalt pavement (RAP) in hot mix asphalt is now common practice in Switzerland. With the increases of RAP content in asphalt mixture, the problematic of the mix design optimization becomes an important issue to be considered. The described project deals with the mix design optimization of hot mix asphalt containing 40 % RAP. In a first phase, an analytical mix design has been conducted. The use of such a numerical method presents in particular the advantages of optimizing laboratory testing and allowing the realization of sensitivity analysis. An extensive laboratory study has been conducted in a second phase. This study permitted to clearly identify and quantify the impacts of the aggregates quality and binder content on the final mixture performances. The various tests achieved highlighted that rutting susceptibility is one of the suitable indicators for the assessment of a mix design performances. The research carried out finally permitted to highlight the benefits of an analytical mix design in a mixture optimization process. The major factors influencing the mix design have been identified and quantified through laboratory testing and some recommendations concerning the tests to carry out are also provided.