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Introduction: The reported 12 months prevalence of low back pain in nurses ranges from 43% to 76%. In most researches physical factors were only a part of high prevalence of low back pain in nurses. This study was conducted to determine the association between occupational stress and low back pain in nurses. Materials and Methods: In this case-control study, 80 nurses as case group and 80 nurses as control group were selected via convenience sampling. Case group were defined as those subjects who had experienced low back pain in the last 12 months. Control group were defined as those subjects who had not experienced low back pain in the last 12 months. A questionnaire was used for data collection which consistsed of 3 sections: demographic information, history of low back pain and occupational stress. Data was analyzed using paired T, Mann-Whitney, and Chi-square tests, correlation coefficient and one way ANOVA Results: Results indicated that, there was an association between low back pain and occupational stress (p<0/01).Also an association existed between low back pain and working hours per month (p<0/05). Statistical tests showed no significant difference between the two groups in terms of age, gender, marital status, number of childbirth, number of pregnancy, smoking, sport, work shift, number of years spent in the hospital (nursing experience). Conclusion: Results indicated that occupational stress in case group was more than control group. Since there was not any significant difference between other factors and low back pain, it can be concluded that there is an association between low back pain and occupational stress.