An appeal court in Cairo has dismissed an appeal against a ban on the Muslim Brotherhood and all its activities, Judicial sources said.
Wednesday's decision is expected to further heighten tensions between the group and the interim authorities, and to diminish chances of a rapprochement.
On 23 September, a court banned the Brotherhood, Egypt's oldest and largest Islamist organisation, and ordered the seizure of its assets and funds.
It also outlawed any institution connected to the Brotherhood.
A lawyer from the leftist Tagammu party filed the case on the grounds of protecting Egyptians from "violence" carried out by members of the group.
The Islamist movement slammed the verdict as "politically motivated" and an "attempt by military leaders" to stifle dissent.
Islamist backers of Mohamed Morsi – a longtime Brotherhood member – have decried his ouster on 3 July as a military coup and an attack on the democratic gains of the 2011 popular revolt.
The Brotherhood has been battered by the fiercest crackdown in its 85-year history. Hundreds of members have been killed and thousands arrested since Morsi's removal.
The group won successive elections following the overthrow of Hosni Mubarak after operating in the shadows for decades under successive authoritarian governments.
Morsi, Egypt's first freely elected president, was toppled after a troubled year in power when many Egyptians, disenchanted with his sweeping powers and mismanagement of the economy, took to the streets to demand his resignation.
The Brotherhood was officially dissolved by the country's military rulers in 1954, but operated underground for decades as the country's largest opposition group. It also focused attention on preaching, and social and charity work.