Tree mortality and turn it to the snag or logs is one of the most important processes in forest ecosystems. Dead trees are an important characteristic of natural forests structure, especially in the old-growth developmental phases which play a wide range of ecological functions. This study aimed to investigate the mortality of trees in the Afratakhteh forest reserve in the Aliabad region. After the preliminary filed observation, three one-hectare study areas were selected and the quantitative and qualitative characteristics (diameter, height, type, and decay stage) of all dead trees were assessed. Results showed that the average volume of dead trees in the study area was 50.44 cubic meter per hectare.  The yew encompassed the high amount of dead volume (37.40 m³) and the most of dead trees were in the second stage of decay. Tree mortality rate in diameter classes showed the greatest amount of dead volume observed in 25-50 cm diameter classes and the highest mortality of yew trees occurred in 10 cm diameter class that are equal to around 38% of total dead volume. Due to the fact that the Yew species are in the red list of threatened species, and on the other hand, the highest mortality rate of this species is observed in low diameter classes, it is necessary to identify the factors that affect its mortality to provide restoration and conservation of yew.