Appleton Academy in Wyke, a through school for students aged 3-18, has shut both its primary and secondary sites.
The bug is thought to be a form of norovirus.
The school posted a Tweet updating parents about the situation:
"Due to sickness bug and increasing number of children and staff having to leave school today, Appleton Aacademy has to take decision to close early. Primary closed 12.30pm - secondary 1pm. Please note we are very busy and short-staffed. We sincerely apologise for the inconvenience."