يقدم البحث دراسة لدرهمين للخليفة العباسي المهدي بتاريخ ضرب سنة 169هــ ، ينشران لأول مرة . ومن المعروف أن الخليفة المهدي قد توفى في 22 محرم مستهل عام 169 ه، وقد تعددت روايات المؤرخين في سبب وفاته، وفي ضوء دراسة هذين الدرهمين وغيرهما من دراهم الخليفة المهدي، يتضح أنه أول من وضع اسم ابنه الهادي کولي للعهد، وحينما تغير مع ابنه خلعه من ولاية العهد ورفع اسمه من السکة، ولذا فإن دراسة دراهم هذه الفترة تلقي الضوء على رأى جديد في وفاة الخليفة المهدي ودور زوجته الخيزران وابنه الهادي في ذلک =The research is a study of two Dirhams of the Abbasid Caliph Al Mahdi. In the research, these two Dirhams that are dated 1690 AH are to be put out in public for the first time. It is known that Caliph Al Mahdi passed away in 22 Muharram at the beginning of year 169 AH and there were several stories by historians regarding his death. This study examines these Dirhams along with several other Caliphs' Dirhams. It became obvious that Caliph Al Mahdi was the first to put his son's name (Al Hadi) as the crown prince. However when the Caliph turned against him, he ousted the crown prince from the covenant and removed his name from roads. Therefore, examining these dirhams sheds light on a new perspective regarding the Caliph's death and the role of his wife Al-Khayzuran and his son Al Hadi in his death.