Drimnagh Castle Secondary School (Irish: Meánscoil Iognáid Rís) is a Christian Brothers secondary school located on the Long Mile Road in the suburb of Drimnagh, Dublin, Ireland. The school buildings are situated directly beside the old Norman castle, Drimnagh Castle, from which the school takes its name.

Drimnagh Castle Secondary School first opened its doors in 1954. For a short time after the school opened, classes took place in the castle itself, until the current buildings were completed at a cost of £84,000.

At the time of its opening, all students were taught by Christian Brothers. Corporal punishment, while legal, was used frequently and with some vigour. The school was not free of sexual abuse during the decades when it proliferated in Irish society. As the years passed the numbers of brothers teaching in the school gradually fell, and there are currently none. The majority of students come from Drimnagh Castle Primary School, but some come from other schools in the area as well as other schools in the surrounding suburbs. Dr Ray Walsh retired as principal in 2013. The current principal is John Hayes.

The school celebrated its 50th anniversary in 2004. The occasion was celebrated by the addition of a new sports changing facility which was officially opened on 4 October 2004 by President Mary McAleese.

Drimnagh Castle Secondary School was identified in September 2024 in the Scoping Inquiry report into sexual abuse in schools run by religious orders. The report cited 14 allegations involving 6 alleged abusers in respect of the school.

• Frank Clarke, judge
• Eamonn Coghlan, senator and former athlete
• Kevin Moran, footballer
• Rick O'Shea, radio personality
• Niall Quinn, footballer and businessman

• Official website