Over fifty formal complaints were made at Castlerea jail last year.
New figures published by the journalist Ken Foxe and The Story.ie reveal that five of the complaints were deemed at the highest scale of seriousness.
These relate to assault, ill-treatment, racial discrimination, or intimidation.
The majority of complaints, 31, were in category C which relates to Basic service level issues (which may include complaints about visits, phone calls, reception issues, missing clothes, not getting post on time or not getting appropriate exercise.
Overall, prisoners made more than 900 formal complaints last year.