Correctional Service Canada says a member of the staff was assaulted at the Kent Maximum Security Institution.
The federal agency says the staff member was taken to an outside hospital to be treated and evaluated.
The attacker has been identified, and R-C-M-P officers are joining the facility's in-house staff in investigating the incident.
Correctional Service Canada says safety of staff and the public remains the highest priority for the agency, and a review will take place to prevent similar incidents from happening in the future.