Socialist MSP Rosie Kane has been released from jail after spending seven "very difficult" days behind bars.
Rosie Kane now plans to campaign on conditions in prisons
The 45-year-old was jailed for refusing to pay a £300 fine imposed over an anti-nuclear demonstration.
She walked free at about 0930 GMT after serving half her sentence at Cornton Vale Prison in Stirling.
It was the first time she had been imprisoned. She said: "It was definitely tough in there but I'm all right. It was worse than I expected."
Ms Kane was greeted by a handful of Scottish Socialist Party supporters, including fellow MSP and one-time Cornton Vale inmate Carolyn Leckie.
She said it had left her with no regrets about refusing to pay her fine.
'No crime committed'
The mother-of-two said: "The women I was locked up with were mostly young and had substance abuse problems and there were no activities at all to do during my stay.
"As tough as it was for me it's much tougher for other women who are drug addicts and have dependant children."
Ms Kane was imprisoned after refusing to pay a fine imposed after being arrested in March last year during a protest in a model submarine outside the Scottish Parliament.
She was convicted of blocking the road and obstructing police. Ms Kane said she had committed no crime.
Ms Kane said she would now campaign on prison conditions.