Alaa Abdel-Fattah walked free from a Cairo police station on Thursday after being detained on May 7 with 10 other pro-democracy activists during a rally outside a Cairo court.
The website - www.manalaa.net - has become an internet base for Egyptian political activists.
It posts announcements of demonstrations, political commentary and photographs of plainclothes security offers notorious for beating protesters.
Abdel-Fattah runs the website with his wife Manal Hassan, who said she was "very happy" that her husband had been released
Hassan said that her husband reported that Wednesday night in the police station was "the most terrible night in six weeks".
"He wasn't tortured exactly, because security officials never touched him, but they threw him into a pen with a large number of hardened criminals who kept him up all night," said Leila Soueif, Abdel-Fattah's mother.
While in prison, Abdel-Fattah continued to post messages on site, using the visits of family members to smuggle out hand-written messages.
After Abdel-Fattah's release order was issued on Tuesday, his wife wrote the blog: "It was the happiest time, and I was chanting 'Down with [President] Hosni Mubarak, as Alaa was taken back from the prosecutors' office to prison."
His wife and mother said that on Thursday, police told them Abdel-Fattah would remain in custody longer, but the family threatened to stage a protest outside the police station.
Egypt has cracked down on protests in recent months, arresting more than 600 demonstrators and drawing criticism from the US and human rights groups.