Fragmentation is one of the major spatial processes leading to change in a landscape, which is described as transformation of a specific habitat or land cover to smaller patches with less connectivity and viability. Construction of Roads is one of the main causes of fragmentation in natural areas and habitats. Presence of roads in ecologically sensitive and protected areas, leads to destruction of values and proper functions of such areas. In Iran, one famous example of this phenomenon is the existing road in Golestan national park. Although this road was destroyed in flash floods due to improper location (close to river) it is still under operation and construction in the same place. This research aims to present a quantitative measure for illustrating the road’s negative impacts on the park by use of one landscape ecological metric. Effective mesh size (meff) is a suitable metric for quantifying fragmentation is which is a probability that two randomly chosen points in the landscape are connected and not separated by barriers and so is a helpful tool for investigating roads impacts on landscapes. In this research, in order to investigate structural changes due to the road, road effect zone was chosen as spatial unit and the metric was calculated for two time series land cover map (1987 and 2008). The results show a decline of 47.40 percent which is an indication of increasing in fragmentation and reduction in connectivity in forest land covers in road effect zone in Golestan national park. Because of high ecological sensitivity of the forest land covers in road effect zone, monitoring their changes should be noticed in management plan of Golestan national park.