Background: Oral hygiene is the practice of keeping the mouth and teeth clean to prevent dental problems, especially dental caries, gingivitis and bad breath. The purpose of maintaining oral hygiene is to prevent the build-up of plaque.  Aim of this study was to assess the oral hygiene knowledge andpractices among school age children. The research design was a descriptive.  It was carried out at 5 governmental primary schools representing Port-Said City. The study subjects consisted of 202 school age children in the age group of 10-12 years, regardless their gender and residence. The data was collected using an interview questionnaire sheet and observational checklist to assess the study subjects' knowledge and reported practices related to oral hygiene. The results of the study revealed that one third of the studied children were at the age group of 11 years, more than half were females. Moreover,  less than half and  more than one third of studied  children had unsatisfactory total knowledge and reported practices respectively regarding oral hygiene. In addition to more than half  of studied  children's  don`t follow up about their teeth. It was concluded that knowledge and reported practices of the studied children regarding oral hygiene practice was satisfactory by more than half of them. The study recommended raising awareness of school age children about oral health and hygiene through oral health education sessions and community outreach programs in children's school settings.