This study attempts to determine the relation of social capital with the development of organizational trust and job attachment among the nurses of the non-governmental medical-treatment service centers of Isfahan city. The study is a descriptive correlational research. The statistical population comprises all the nurses of the non-governmental medical treatment service centers of Isfahan city between the years 2009 ? 2010. 112 nurses were selected by employing cluster random sampling. For data analysis, Pearson's correlation coefficient and multiple correlations were adopted. For data collection, the study uses three questionnaires (Roder's organizational trust questionnaire, 2003; the researcher-made questionnaire of job attachment; and the researcher-made questionnaire of social capital) whose validities are measured respectively at 0.87, 0.89, and 0.91 in terms of the obtained content and according to Cronbach's alpha. Generally, the findings reveal that , the structural aspect alone accounts for 51 percent of the variance of organizational trust which is increased by the cognitive aspect up to 56 percent and goes up as far as 64 percent by considering the communicational aspect. Besides, the findings also reveal that the structural aspect alone accounts for 47 percent of the variance of job attachment which is increased by the cognitive aspect up to 54 percent and goes up to 58 percent by considering the communicational aspect. Key words: social capital, organizational trust, job attachment, medical-treatment service centers.