Gamma rays pose enough energy to remove electrons from atoms of absorbing material including human body and adversely affect human health. The external exposure of human beings to natural environmental Gamma radiation normally exceeds that from all man-made sources combined. Therefore, we monitored Gamma dose rate in indoor environments and estimated corresponding annual effective dose in selected districts of Ardabil Province, Iran. Indoor environmental Gamma dose rates were measured using an Ion Chamber Survey Meter, FLuke-451b, in 88 selected dwellings (One in city center and the remaining in cardinal and ordinal directions with an appropriate distance from each other) in Ardabil, Sar Ein, Germy and Kosar. The measurements of Gamma radiation dose rate were performed at 20 and 100 cm above the ground for a period of one hour. Average absorbed dose rate (i.e. arithmetic average of dose rate at 20 and 100 cm above the ground) inside buildings for Ardabil, Sar-Ein, Germy, and Kosar were 238, 221, 402, and 361 nSvh-1, respectively. The respective corresponding values for annual affective absorbed dose rate due to indoor environments for the studied area were 1.17, 1.08, 1.97, and 1.77 mSv, respectively. Calculated annual effective doses for selected districts of Ardabil Province were appreciably higher than the population weighted average exposure to environmental Gamma radiation worldwide as well as the average estimated value for Iran.