Forests as one of the most important terrestrial ecosystems provide many ecosystem services that almost there is no market to present their values. Among this non market services, gas regulation has a significant importance. Plants absorb co2 and use it in photosynthesis process. This process, in addition to producing plant biomass and releasing o2, has the effective role in reducing the greenhouse effect. There is not a spatial similarity in co2 absorption in an area, according to difference in plant concentration, tropical situation, kinds of specious and plants growth per hectare. In this case study we create a pattern to archive spatial distribution of co2 absorption with geographical information system in a part of Caspian forests of Iran. In this pattern according to kinds of specious, plant concentration and growth per hectare we achieve the map of spatial distribution of co2 absorption value. Planners can Use this map, as a decision support tools, for more careful local and regional planning. The co2 absorption services has been valued with replacement cost method that is one of the most significant cost based methods in environmental economic. Results show that in the study region with an area of 20582 hectare, the value of co2 absorption is more than 80 billion Rials per year.