South Australian senator Penny Wright has announced she is resigning because of an illness in her family.

Senator Wright was elected in 2010 and said she was proud of what the party had achieved so far.

"I have thought very carefully about this step," she said.

"I am disappointed to be leaving the Senate and my colleagues but I know that this is the right decision for my family and me."

She said she would remain in the role until the Greens chose a successor to "fill the casual vacancy and contest the next election".

Greens leader Richard Di Natale said he understood Ms Wright's reasons and fully supported her decision.

"Penny has made an enormous contribution during her time as an Australian Greens senator for South Australia and I speak for all of my colleagues when I say she will be sorely missed," he said.

Ms Wright said her proudest achievements included introducing "the concept of justice reinvestment" to South Australia, to "reduce the disproportionate rate of Aboriginal people in our jails".

"I am also proud of advocating for the mental health needs of rural people throughout Australia," she said.

She said her other achievements included helping the Kangaroo Island community to "protect the environment and economy against oil and gas exploration", and helping peacekeepers "secure their right be acknowledged on the honour roll of the Australian War Memorial".

Ms Wright said she had also defended human rights "in the face of relentless attack by both Labor and Coalition governments in the name of so-called border protection and national security".