Background: the prevalence of gadget was increased between university students. They use it for entertainment rather than learning. The long use of smartphone would be risk factor to musculoskeletal disorder, early neck pain, neck problems and poor work habits that load cervical region. Purpose: this study was conducted to study the effect of smartphone addiction on cervical range of motion and neck function among undergraduate students in the faculties of physical therapy. Design: Cross-sectional one–shot, controlled observational study. Methods: one hundred students selected from different physical therapy colleges in Cairo and Giza using short version of smartphone addiction scale (SAS sv). For selection, the students were assigned into two groups; Group A, consisted of 62 students who were non–addicted smartphone users and Group B, consisted of 38 students who were addicted smartphone users. Cervical range of motion (ROM) assessed by CROM and Copenhagen neck function disability index was used to assess neck function. Result: There were no statistical significant differences between both groups regarding BMI., regard to the cervical range of motion there were statistical significant differences between both group in all direction (flexion, left lateral flexion, right lateral flexion, left rotation and right rotation) except extension and Copenhagen neck functional disability index was significantly higher among smartphone addicted group. Conclusion: Smartphone addiction affects cervical range of motion and neck function so, it is recommended that physical therapy students should not use smartphone in addicted manner to prevent long term neck disability. Ergonomics advises for smartphone use will be preventive therapy programmers.