Abstract: Objectives: Joint Hyper-Mobility is an important and occult joint involvement in normal population. We studied to determine the prevalence and features of JHM in Iranian students. Methods: A group of Iranian primary to high school students in Tehran was considered in the figure of a cross sectional-descriptive study. Though validated Carter-Wilkinson & Beighton criteria 997 students from five geographical regions were screened. Sampling method was Randomized - multi process. We had accepted Score higher than four as generalized JHM. Results: The prevalence of JHM was 15.7%; JHM was significantly more common in female (18.5%) than male (13%), P=0.02. The difference between prevalence in primary school (mean age 8.8 years) and high school (mean age 15.1 years) students was significant (18.2% versus 13.3%), P=0.03. The main involved joints were as follow: thumb, fingers, knee and lumbosacral joints. There was a few difference between involvement in two sexes, so the knee involvement in girls and lumbo-sacral in boys were seen less than other joints. The JHM was seen significantly more frequent in non-dominant side fingers, P<0.05. Conclusion: JHM is a common finding in Iranian students. It is more frequent in female than male. The most common site of involvement is thumbs joint.