Socialist MSP Carolyn Leckie has been released from prison after spending a night behind bars after refusing to pay a fine.
The controversial MSP said the experience was dehumanising
Ms Leckie was arrested during a demonstration at Faslane Naval Base in August 2004 and unsuccessfully appealed a breach of the peace conviction.
She said she now wanted to campaign for better conditions for prisoners.
The MSP will raise her concerns with the justice minister and the Scottish Prison Service.
Ms Leckie added that she had no regrets and would repeat the experience if necessary.
Emerging from the gates of Cornton Vale women's prison in Stirling, Ms Leckie said: "My overwhelming impression is that the penal system is exactly that - punishment.
"There is certainly not enough done to give hope to the women in there.
"I was there with the luxury of spending just one night there on a point of principle but the vast majority of women are put there through poverty - and that is an absolute shame."
Ms Leckie, 39, was jailed for seven days on Thursday after refusing to pay a £100 fine.
But because short-term prisoners serve only half their sentence, and prisoners cannot be discharged over the weekend, she was released, having spent just one night in the jail.
Ms Leckie emerged from the prison to be greeted with a huge hug from her waiting daughter Ailidh, 15, and from two fellow SSP MSPs, Rosie Kane and Frances Curran.
The MSP said she had no complaints at her own treatment but was critical of the system in general, which she claimed was there to humiliate prisoners.
She told how, after being processed on arrival at the prison, her clothing was taken and she was issued with tracksuit bottoms and a sweatshirt.
Dinner last night was boiled potatoes, mushy peas and shepherd's pie and after an evening of reading, watching TV and talking to other women, she was locked in her cell from 2100 GMT to 0745 GMT.
Ms Leckie was jailed over protesting at the Faslane Naval Base
She said personal possessions were needlessly removed from the arriving women prisoners, including moisturiser.
"Every woman uses moisturiser and I really don't see the need to have it withdrawn," she said.
She described how there were no locks on the toilets or the showers and the doors filled only half the door space.
"I think I'm lucky to have only spent one night there, that has to be said," said Ms Leckie.
She added: "Conditions were very basic and sparse, the staff were very nice and respectful, but the whole system is geared to dehumanising, humiliating and punishing people and crushing their spirit."
Conservative chief whip Bill Aitken said: "If Ms Leckie wishes to make herself a martyr, the system should not allow her to do so.
"This outlines the reason why fines should be deducted from salaries and benefits, which would have the dual benefit of ensuring that all fines are paid and that prisons are not cluttered up with those who do not need to be there - such as Ms Leckie who is simply using the entire issue as propaganda."