Introduction: Nausea and Vomiting due to chemotherapy are the most distressing side effects of this treatment in breast cancer patients. Apart from pharmacological factors, non-pharmacological factors including psychological factors such as emotions and emotion regulation have a significant impact on the incidence and severity of these side effects. Because emotion regulation is one of the main factors leading to different behaviors in different individuals in response to various situations, the aim of this research is the study of difficulties in emotion regulation as a predictor of incidence and severity of nausea and vomiting in breast cancer patients.
 Materials and Methods: In this is descriptive correlation study (Oct 2012-Feb 2013), 300 breast cancer patients referred to Reza clinic and Omid and Qaem hospitals in Mashhad were selected through available sampling. They completed Difficulties in Emotion Regulation Scale (DERS) and nausea and vomiting scale (MANE). To data analysis SPSS software, factor analysis and regression analysis were used.
 Results: The results of regression analysis showed that difficulties in emotion regulation can predict the incidence and severity of nausea and vomiting in breast cancer patients (P<0.01).
 Conclusion: Considering the findings, difficulties in emotion regulation can predict the incidence and severity of nausea and vomiting in breast cancer patients.