The blaze was reported shortly before 5am at a home on Monastery Grove in Enniskerry, Co Wicklow.
Gardai said two children aged 15 and 13 fled from the house and suffered only minor injuries.
The woman was found dead in an upstairs room of the home.
Gardai are carrying out a technical examination of the scene but the fire is not being treated as suspicious.
The two children were treated at Crumlin children's hospital.
COMMENT RULES: Comments that are judged to be defamatory, abusive or in bad taste are not acceptable and contributors who consistently fall below certain criteria will be permanently blacklisted. The moderator will not enter into debate with individual contributors and the moderator’s decision is final. It is Belfast Telegraph policy to close comments on court cases, tribunals and active legal investigations. We may also close comments on articles which are being targeted for abuse. Problems with commenting? firstname.lastname@example.org