Rock slope instabilities are a major hazard for human activities often causing economic losses, property damages and maintenance costs, as well as injuries or fatalities. For slope stability analysis of open pit mines, series of studies must be carried out in order to identify the criteria which should take into consideration. In this research geotechnical parameters; Geological Strength Index (GSI), Rock Quality Designation (RQD), Cohesion (C), angle of internal friction (phi), uniaxial compressive strength (UCS) and Rock mass deformation modulus (E (m) ) which are obtained from data measured within geotechnical boreholes and pore pressure (U) are considered as the criteria to evaluate stability of pit No.1 of the Gole Gohar iron mine, located in Kerman province, south east of Iran. Since human judgments and preferences are often vague and complex and decision makers cannot estimate their preferences with an exact scale, we can only give linguistic assessments instead of exact ones. So fuzzy set theory introduced into Analytical Hierarchy Process (AHP). Fuzzy AHP (FAHP) is put forward to solve such uncertain problems. In this paper, FAHP method is used to determine the weights of the criteria by decision makers and then classification of the stability of blocks are determined by TOPSIS (Technique for Order Preference by Similarity to Ideal Solution) method by the shortest distance to positive ideal solution (PIS) and the longest distance to negative ideal solution (NIS).
