This research carried out with the aim of studying the mediating role of self – esteem on the relationship between perceived organizational support and self – efficacy. Research method was correlational and statistical population was all employees of Isfahan province Gas Company. Using convenience sampling, 248 subjects were selected.  They were assessed by perceived organizational support questionnaire (Eisenberger et al.), self - esteem questionnaire (Rosenberg) and self - efficacy questionnaire (Sheerer & Maddux). Data were analyzed by use of Pearson correlation coefficient and Structural Equation Modeling. Results showed that there was significant relationship between Perceived organizational support and self - efficacy (p<0.01), Perceived organizational support and self - esteem (p<0.01) self - esteem and self - efficacy (p<0.01). Moreover results of Structural Equation Modeling showed that self – esteem played a mediating role between perceived organizational support and self – efficacy (p<0.01). According to these findings, for increasing of employees’ self – efficacy in organizations, should pay more attention to employees’ self – esteem through organizational support.