The present paper investigates the stochastic seismic responses of steel Structure systems with Partially Restrained (PR) connections-by using Perturbation based Stochastic Finite Element (PSFEM) method. A stiffness matrix formulation of steel systems with PR connections and PSFEM and MCS formulations of structural systems are given. Based oil the formulation, a computer program in FORTRAN language has been developed, and stochastic seismic analyses of steel frame and bridge systems have been perlormed for different types of connections. The connection parameters, material and geometrical properties are assumed to be random variables in the analyses. The Kocaeli earthquake occurred in 1999 is considered as a around motion The connection parameters., material and geometrical properties are considered to be random variables. The efficiency and accuracy of the proposed SFEM algorithm are validated by comparison with results of Monte Carlo simulation (MCS) method.