Background: Primary dysmenorrhea disturbs the quality of life of nursing students females. It decreases students' academic performance, peers class concentration and increase absenteeism. Aim of the study: The present study aimed to assess knowledge regarding primary dysmenorrhea among nursing students. Research Design: Descriptive study design was utilized in this study. Setting: The study was conducted at Faculty of Nursing Benha University. Sample: A purposive sample of 100 students in the first academic year. Tools of data collection: Two tools were used, Tool (I): Self- administered questionnaire sheet. Tool (II) Nursing students Knowledge regarding dysmenorrhea. Results: 48% of studied students aged (18:<19) years with the mean and SD 17.76±0.68, weight of studied students ranged from 42-85 with the mean and SD 58.07±7.50, while the height ranged from 145-180 with the mean and SD 157.38±8.22, and 59% of them had normal body mass index with the mean 23.57±3.51. 72% of studied students had menarche at age 12-14 years with the mean ±SD of 13.19±0.62, while 94% of students menstruated 4-6 days with the mean ±SD of 5.101±0.7213, and all students had regular menstruation with interval from 21-35 days while 64% of students had moderate follow of menstruation. Conclusion: The study concluded that the majority of studied nursing students had poor knowledge about primary dysmenorrhea. Recommendation: Implement targeted educational programs to enhance nursing students' knowledge about primary dysmenorrhea, including its causes, symptoms, and treatment options.