Using of Reclaimed Asphalt Pavement (RAP) has been become indispensable in most of the world nations as for its many benefits as significant cost savings and provide environmental benefits. Many factors such as virgin materials, binder content, availability of RAP, viscosity of binder and extent of deterioration had important role in effecting on Optimum percentage of RAP. In this study, effect of using RAP on the asphalt mixture properties and the its optimum ratio was determined to achieve the objective of the study. The glass fiber (GS) was used as additives to improve the asphalt mixture. It has been observed from the previous researches that the optimum percentage of reclaimed asphalt use is not determiner and is disagreed from project to project. So, different percentages of RAP was (25%, 50%, 75%, 100%) by weight of aggregate were added as well as using the additive GS at optimum bitumen content. The study is revealed that untreated 100% RAP materials are not good as a bituminous mix. and was showed that mix prepared with 25% RAP gave nearly the same physical and strength parameters as virgin bituminous mix. From results of study, the use of RAP until (%50) as a maximum percentage in unmodified asphalt mixture course sustained good results. To achieve better performance, the percentage of 25% RAP was used with percentage of 0.26% GS. This mix achieved the specification requirements and ensured the degree of better performance for paving. The economical evaluation of using percentage of 25% RAP with percentage of 0.26% GS was also studied. The results indicated that, about 21% of the cost was saved. Keywords: Reclaimed Asphalt Pavement (RAP), Marshall Mix Design, Material Testing, Stability, Glass fiber, Optimum Bitumen Content, Cost effectiveness.