Abstarct: Usually, design codes are codified in a way that also satisfy the safety conditions, but also bring economic design. This desired can be achieved with combination of theoretical relations and experimental results and safety factors. Safety factors is rooted in probability studies which are determined according to reliability theory. Standard codification committees, considering the random nature of factor involved in the design relations and economic design in order to present design formulas. How to deal with probabilistic factors, cause different design methods such as allowable stress and limit states and etc. Since the current steel code of Iran is similar to American, can noted the load combination and design relations, this suspicion creates that the criteria for design of Iran steel code adapted well to the probabilistic conditions of Iran or not? In this thesis particularly, the sefaty level of steel beam-columns under biaxial bending is studied. For this purpose, a program is written that determines the probability of failure of this beam-columns in 3-D frxames baxsed on monte carlo method. Also a program that with existing limit state function can determine reliability index is written baxse on analytical methods. The obtained results show that beam-columns designed baxsed on Iran code, in gravity load combinations is well at safety and a bit non-economic, in load combinations with Presence of wind load safety level is very high and non-economic, in load combinations with Presence of earthquake load safety level is a bit lower than required.