South Australian Liberal Senator Mary Jo Fisher has announced she is quitting Parliament after again being reported for shoplifting.

Senator Fisher has released a statement saying she will quit Parliament in August on medical advice after experiencing a panic attack similar to one that she suffered 18 months ago.

She will be summonsed over the incident, that is alleged to have taken place at a supermarket in Adelaide's west on Saturday.

Security officers allegedly found goods in Senator Fisher's bags that had not been paid for.

Senator Fisher was accused of stealing $92 worth of groceries from a Foodland store in December 2010, and pushing a security officer who approached her in the car park.

Late last year she was acquitted of the resulting shoplifting charge but found guilty of assault and released without conviction.

Announcing she was retiring from politics, Senator Fisher said serving in the Senate was not helping her recovery from her depressive illness.

But she also blamed "dogged, calculated and deliberate attempts by the police prosecution service" to extend her "emotional turmoil".

"I am today announcing my intention to resign my position as a senator representing the people of South Australia, effective August 10," she said in a statement.

"It has become undeniable that for me, the road to full recovery from my depressive illness has been hampered by my trying to get better, at the same time as continuing to serve in public office.

"My faltering recovery was exacerbated by repeated pressures from dogged, calculated and deliberate attempts by the police prosecution service to do everything possible to increase the length, complexity, cost and emotional turmoil both of my recent and extended trial, and the subsequent and continuing post-trial cost processes."

Former Liberal senator Nick Minchin says he is saddened by Senator Fisher's decision to quit.

Mr Minchin was one of her strongest supporters when she entered Parliament in 2007.

"I'm quite distressed by the news tonight that Senator Fisher has decided to resign after another incident," he said.

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"She's a highly intelligent and very capable woman who's given great service to South Australia and to the Liberal Party and to rural constituencies in particular, and I'm really very saddened by tonight's news."

Senator Fisher thanked her family and staff for their support, saying it was an honour to represent the people of South Australia.