Abstract: A pulling effect by side roots is one way in which roots help to side in-plane strong of a little depth soil mass. In contrast to the effect of vertically-enlarge roots, whereby soil is strengthened by an increase in its shear strength, the pulling effect strengthens the soil by increasing the tensile strength of the rooted soil zone. To verify whether or not a pulling effect exists in the root system of Oak (Quercus castaneaefolia L.) in the Roudsar, N Iran and to study the importance and size of this effect, a direct in situ test was led at a site in the Rahimabad Forests. The results from the site showed that, in the surface soil (0-35 cm), Side roots can provide a pull force of up to 264.61 N (Newton) over a vertical cross-section area of 20-50 cm2, or enhance in the pulling stability of the rooted soil by 30.96%. The test results suggest that, together with the Oak vertical roots, which keep the little depth rooted soil zone to the deep and more stable soil mass, the side roots of the Oak, with their pulling effect, are able to make less against little depth instability in the forest slopes, such as little depth slide, to a certain degree.