The crackdown comes even as the kingdom breaks with long-held restrictions on women's lives, preparing to lift the world's only ban on female motorists on Sunday.
That was a goal some of the detainees had championed for decades, but credit for the policy change has gone to young Crown Prince Mohammed bin Salman, architect of an aggressively marketed reform package.
Some of those detained have since been released.
But for Saudi activists, their arrests confirmed that even if the monarchy dictates the easing of some social restrictions, it will resist granting any modicum of democracy.
Saudi Arabia arrests more women's rights activists- HRW
Three of the most prominent figures who continue to languish in detention are Loujain al-Hathloul, Aziza al-Yousef, and Ibrahim al-Modaimegh.
Loujain al-Hathloul was among a group of women's rights activists arrested in mid-May.
The 28-year-old has long campaigned for women to be able to drive and an end to the kingdom's notorious guardianship system, which requires women to get permission from male relatives for many decisions.
This was not the first time Hathloul, from the conservative central region of Al-Qassim, has been behind bars.
Saudi authorities put her in juvenile detention in late 2014 when she tried to drive into the kingdom from the neighbouring United Arab Emirates.
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Hathloul was freed 73 days later following an international campaign.
Her most recent arrest triggered a smear campaign in the pro-government press, which printed her photo along with those of fellow feminists, branding them 'traitors'.
Another activist, who declined to be named over fears for her family's safety, told AFP that Hathloul represented Saudi Arabia's modern feminists.
"Loujain is the young rebel woman from Al-Qassim who embodies global values... and calls out the (lies) of the state," she said.
On May 19, Hathloul's face was printed on the cover of Saudi Arabia's Al-Jazirah newspaper, alongside fellow activist Aziza al-Yousef, with the headline: "Your betrayal has failed".
If Loujain al-Hathloul represents Saudi Arabia's young, outward-looking feminists, fellow activists say Aziza al-Yousef embodies an older generation of trailblazers.
Yousef, 61, was one of a small number of women who responded to calls to defy the kingdom's driving ban in 2013 and again in 2014.
The retired university professor in 2016 attempted to deliver a petition to the Royal Court, signed by thousands of Saudis, demanding an end to the guardianship system that gives men control over their female relatives' rights to study, marriage and travel.
Yousef has also spoken out against domestic violence, condemning the "lenient" eight-year sentence handed to a Saudi preacher convicted of raping and killing his young daughter in 2011.
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Unlike many of her younger counterparts, Yousef expresses her arguments for women's rights through the lens of Islam.
"Aziza is different. She's wearing her (head) scarf. She's speaking the language of the traditional. She represents a unique model that is tolerant to all," a fellow activist said.
"That's why the Saudi state is angry. She embodies both progressive and traditional norms."
While younger campaigners are dismissed by some as products of Westernisation, out of touch with their religion, Yousef maintains her religious credentials, the activist said.
"Aziza is very much committed to Islam," she added. "She talked about how Islam respected women."
Attorney Ibrahim al-Modaimegh has come out of retirement in recent years to defend his fellow feminists.
As a senior legal figure, he was long protected by his stature, other activists say.
He had served on the kingdom's top legislative councils and helped draft many of its laws.
"He retired about seven years ago, but he has taken on almost all of the activists' cases," a Saudi activist told AFP on condition of anonymity.
The respected lawyer worked particularly hard to defend women who defied the kingdom's notorious driving ban.
"That was one thing the government seems really angry about," the activist said.
In mid-May, he was swept up in the crackdown on feminists he had spent years defending, with the pro-government press branding him "the devil's advocate".
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