Introduction: Reforms in nursing clinical error-reporting system is of great importance in health care systems. This study aimed to determine the factors affecting the incidence of nursing errors using the theory of planned behavior constructs.

Method: In this descriptive-analytical study, conducted in 2015, 225 nurses were randomly chosen from five public hospitals in karaj. A questionnaire was prepared based on the Icek Ajzen’s Theory of Planned Behavior for data collection, the validity and reliabilty of which was confirmed by experts and piloted among 30 nurses. Cronbach's alpha for questions ranged between 0/610 and 0/885. The data were analyzed by SPSS version 19 using descriptive and inferential statistics.

Findings: Perceived behavioral control from self-reporting error was the strongest factor of nurses’ intention to report clinical errors (r =0 /56; P value <0/05).

There was a significant positive correlation between all variables and the nurses’ intention toward error reporting (except Behavior), the mean scores of which based on their attitudes, perceived behavioral control, and subjective norm were

 5/5± 0/75 , 4/8±1 /04 and 4/4 ± 1/38, respectively.

Conclusion: Clinical errors reporting by nurses are affected by different barriers, social pressures and their motivation to report errors in their systems which will surely affect the quality of health care services.