Although many researchers have focused their attention to man made sources, but natural sources constitute more than 85% of human exposure to ionizing radiation. Due to the significance of natural sources, comprehensive studies have been carried out in developed countries. In Iran like many other developing countries, this subject has not been considered as a research priority. Until 1990 only Ramsar located in the south coast of Caspian sea had attracted attention of some researchers. In 1996 preparation of out-door natural radiation map of Iran was defined as a long term goal in my center. Since then environmental gamma radiation dose rate of residential area of 10 counties have been estimated. In this article only annual dose rates of Khorasan are reported.In every one city five stations were selected. A survey meter model RDS-110 was placed one meter above the ground level.Dose rates were measured for one hour in three successive days. Although average dose rates of every one of the stations were numerically different, but their differences are not significant. Out-door gamma dose rates acquired for 24 towns are within the range of 56 to 144 nGy/h.Minimum and maximum dose rates are respectively attributed to Dargaz, in the north and Gonabad in the south.