Background and Objectives: Job stress is one of the most problematic diseases affecting nurses in hospital environments. Early maladaptive schemas play a role in job stress. Besides, when schemes are activated, levels of excitement are published, leading directly or indirectly to various forms of psychological distress, such as depression, anxiety, and stress. Therefore, this study aimed to assess the effectiveness of schema-based cognitive therapy in reducing job stress among nurses. Methods: This semi-experimental controlled study with pretest-posttest design was performed on nurses in Qom in 2015. Totally, 32 nurses were selected by simple random sampling and were divided into an intervention (n=16) and a control group (n=16). The intervention group received weekly sessions of cognitive schema techniques for nine weeks. The data were collected using occupational stress questionnaire developed by Davis, Robbins, and MacKay (1991). Then, the data were entered into the SPSS statistical software, version 20 and were analyzed using MANCOVA. Results: The results showed a significant difference between the two groups regarding job stress symptoms and resources after the schema-based cognitive group therapy. Accordingly, symptoms and resources of job stress significantly reduced in the intervention group compared to the control group (p=0.0001). Conclusion: This study showed that schema-based cognitive group therapy was effective in improving the symptoms and resources of job stress. Thus, this therapeutic method is recommended to be used in nurses with job stress.