This study explores issues related to vegetation effects in slope stability analysis. The main objective of this research was to assess the influences of suction in the stability of slopes. A slope inclination of 1:2 was tested in all cases using SLOPE/W which is sophisticated software with useful features, including suction parameter. Therefore, slope stability analysis was achieved with the usage of this sophisticated software so as to simplify the mathematical processes which are time-consuming. The analysis was based on the Mohr-Coulomb equation arranged appropriately so as to include suction effects. Field measurements recorded by Biddle for mature trees placed on clay subsoil were used to measure the suction effects for each case. Overall, a satisfactory association between field data and results was achieved. For the cases considered, it was indicated that moderately small suction changes from 18 to 39 kPa can influence the safety factor against failure of the slope. All of the analyses showed that the slope model was stable in each case, since safety factor ranged from 1.689 to 4.750. Under undrained conditions Gault clay was found to have a minimum safety factor of 2.553. Suction effects were found to increase the stability of slopes. In the unsaturated analysis, it was found that as b j increased the FOS also increased. Moreover, London clay was found to have a minimum FOS of 2.303 when tested with the effects of matric suction.cohesive and consequently τ f =c u where τ f is the shear strength of the soil. Vegetation effects were not taken into account in this type of analysis, since vegetation is correlated with suction and root strength.The fact that clay is purely cohesive under undrained conditions means that no drainage is allowed [2]. According to Craig, circular slips are associated with homogeneous and isotropic conditions of the soil. Failure of the slope could occur because of the weight of the soil above the slip surface. Finally, undrained shear strength ( u c ) was found for the three soil types (Boulder clay, Gault clay and London clay). Due to the fact that the aim of this dissertation is to estimate the minimum safety factor, worst case scenarios were taken into consideration, therefore the worst values of ( u c ) were chosen. Method of slices (Bishop's Simplified Method)Bishop's simplified method was used to analyse the stability of slopes for the next two stages where the cases of unsaturated clays were taken into account. The assumption made in this method is that the tangential interslice forces are equal and oppose each other thus