Introduction: The purpose of this study was to determine the effect of job strain intensity on blood pressure (BP) during nurses' work shifts in the hospitals of Mashad University of Medical Sciences.

Method: For this descriptive cross-sectional study,150 nurses who met the inclusion criteria were chosen by cluster sampling. A questionnaire was used to gather the data including personal charac- teristics, height, weight and intensity of job strain. Blood pressure was measured three times: in the beginning, middle and the end of the work shift.

Results: Women constituted 79% of the participants, and 80% were married . Eighty-nine percent of nurses had a Bachelor’s Degree, and 31% had BMI>25. There was a significant relationship between job strain and age, marital status and the hospital unit where they worked. 

The results imply the significant effect of job strain on the difference in first-second, and second-third systolic BP, but not on differences between diastolic BPs. General linear models indicate a significant relationship between working in emergency unit and first-second systolic BP variations. Marriage and divorce have significant relationship with the first-third systolic BP variations.

Conclusion: In this study job strain had a significant effect on nurses’ systolic BP at shift work.