Abstract Background: The prevalence of Repetitive strain injuries (RSIs) in upper extremities is reported in many countries, but its occurrence among teachers in Egypt has not been reported. Aim of Study: To investigate the prevalence of RSIs in teachers at Giza Schools and to assess the effect of RSIs on the hand and pinch grip strengths. Material and Methods: A sample of 515 teachers has been recruited from secondary schools in Giza. Subjects had 5 or more years of work experience and their age ranged from 35 to 60 years old. Participants were asked to answer the self-structured questionnaire. Hand and pinch grip strengths were measured by hand grip and pinch grip dynamometers. Results: The prevalence of RSIs in Giza school teachers was 89.51%. There was an impact of RSIs on the hand and pinch grip strength. Hand grip strength or pinch grip strength was the highest affected component (86.55%). There was a significant increase in the prevalence of RSIs in the right upper limb 86.6% compared with that the left upper limb 13.4%. The prevalence of RSIs was greater with exceeding many hours per week, elongated manners during schooling, ageing, and among females. Conclusion: There was a highly significant prevalence of RSIs in upper extremities among teachers in Giza schools (p=0.0001). Also, there was a negative impact of RSIs on the hand and pinch grip strengths.