Chants such as "Burn in hell, Abu-Musab al-Zarqawi" were heard from the demonstrators, referring to claims the leader of the al-Qaida in group to have carried out the attacks.
"We sacrifice our lives for you Amman," chanted the protesters at one demonstration, near one of three hotels hit by Wednesday evening's explosions.
Officials said 56 people, mainly Jordanians, were killed in the attacks on Amman's Grand Hyatt, the Radisson SAS and the Days Inn.
"Death to al-Zarqawi, the villain and the traitor," shouted the angry crowd comprising Jordanians of all backgrounds, including women and children.
Drivers of vehicles decorated with the colourful Jordanian flags and posters of Jordan's King Abdullah II honked their horns.
Other rallies were held across the kingdom, including one in the Red Sea port of Aqaba, where attackers using Katyusha rockets narrowly missed a US ship and killed a Jordanian soldier in August.
"We're here to condemn in the strongest terms the heinous crime committed against Jordan by a group of terrorists"
veterinary union president
Others were in al-Zarqawi's hometown of Zarqa and the southern city of Maan.
The Amman protest was organised by Jordan's 14 professional and trade unions, made up of both Islamic groups and leftist political organisations, traditionally a vocal critic of King Abdullah's moderate and pro-western policies.
"We're here to demonstrate our support of our government and express our love to our country and condemn in the strongest terms the heinous crime committed against Jordan by a group of terrorists," said Abdul-Fatah Kilani, president of the veterinary union.
Businessman Muhammad Daoud Mheirat said: "This rotten group and those killers have nothing to do with our religion."
The streets of the capital appeared deserted early on Thursday, which was declared a day of mourning.