Some 24 activists will go on trial in Egypt charged with taking part in an illegal protest, campaigners said.
The detained activists include Sanaa Seif, sister of leftist activist Alaa Abdel Fattah who was recently sentenced to 15 years in absentia.
Dozens of activists were arrested in recent months after a law banning all but police-sanctioned rallies was adopted in November. Activists say the law restricts, rather than regulates protests.
The 24 activists were rounded up while participating in a protest against the law on Saturday. Authorities said the group were arrested because they had not obtained a permit from the Ministry of Interior prior to organising the protest, as the law requires.
One of the detainees is a minor who has been referred to a special court for minors, a lawyer told AFP.
Following the July 3 military coup, Egyptian authorities have launched a relentless crackdown against the main opposition group, the Muslim Brotherhood. The crackdown, however, has gradually extended to secular and leftist activists who protested against human rights violations committed by post-coup governments.