A 65-year-old grandmother who organised a protest in Shanghai demanding better benefits for retirees has been sentenced to three and a half years in jail, a relative and court official said Thursday.

Zhang Weimin was sentenced this week for disturbing public order after she helped organise a peaceful demonstration of hundreds of retirees in the city in November last year, a relative who wished to remain anonymous told AFP.

A spokeswoman for the Shanghai Number Two Intermediate Peoples Court confirmed the sentence.

Zhang is the leader of a group of Shanghai residents -- now retired -- who were sent to the far western region of Xinjiang in the 1960s to work as part of a policy of dispatching so-called "educated youth" to rural areas.

Many returned to the eastern commercial city from Xinjiang in the late 1990s, but they complain their pension and health benefits are lower than other Shanghai retirees.

Although Shanghai residents were sent to many parts of China at the time, the Xinjiang returnees are the best organised and have held weekly protests for nearly a decade, with participants sometimes numbering in the hundreds.

"They targeted her since she was the leader," said the relative, who declined to be named out of fear of reprisals by authorities.

Police also detained scores of supporters who showed up at the courthouse to rally around Zhang at her sentencing on Tuesday.

The charge stems from a protest held last year in People's Square, right outside the city hall in downtown Shanghai.

But Zhang was not detained by police until April this year, when she was arrested amid a crackdown on dissidents, activists and lawyers following revolts in the Arab world.