Anna Maria Cancellieri is accused by critics of using her influence to help ensure Giulia Ligresti, who reportedly suffers from anorexia and anxiety, was moved from prison to house arrest.
"I never requested her release, it was not the result of pressure applied by me," she said in a speech to the upper house of parliament.
Cancellieri said the decision to move Ligresti was made by a court, based on an independent medical examination.
Ligresti was arrested along with her father and sister during a probe into false accounting at insurer Fondiaria-SAI, which her family controlled until last year. Her father was placed under house arrest while she and her sister ended up behind bars.
Cancellieri had earlier admitted asking prison authorities to evaluate Ligresti's health and published transcripts of her phone calls appeared to show her promising the woman's family she would deal with the matter.
She told the Senate she had "acted in the same way as in this case in many other cases... over 100 in the past few months alone", in the face of "an unacceptably high suicide rate in prison".
"Every death in prison is a defeat for the state and the prison system. I feel the weight of the situation and have dedicated a not insignificant part of my time to the prison problem," she said.
The justice minister's critics accuse her of fuelling cronyism and of acting out of a conflict of interest because of her long friendship with the family.
Cancellieri's son, Piergiorgio Peluso, earned several million euros working as an executive at Fondiaria-SAI between 2011 and 2012.
"My personal relationships have never influenced my government work," Cancellieri said