The Bread and Freedom party (Eish we Horria) has been formed by former members of the Socialist Popular Alliance Party (SPAP).
The party's name is part of a popular slogan used during the January 2011 uprising that toppled president Hosni Mubarak.
The party aims to "promote the revolution's values, real development and the redistribution of wealth to the working class."
Former presidential candidate Khaled Ali, one of 280 defectors from the alliance, is yet to join the new party. But he attended a recent meeting to discuss its first six-month plan.
After six months, a general meeting will be held to assess the plan and define future steps, party media officer Mona Ezzat told Al-Ahram's Arabic news website.
Those who resigned from the alliance include Cairo secretary Akram Ismail, Alexandria secretary Suzan Nada, media spokesperson Mona Ezzat, deputy president for political public affairs Emad Attiya, and central committee member Elham Eidaros.
In a statement, they expressed dissatisfaction with the alliance's recent internal elections. They also criticised its "failure to formulate a political stance" post-30 June, adding that a domineering group within the alliance had blindly followed the state.
The alliance has supported the transitional roadmap announced by the interim authorities following president Mohamed Morsi's ouster in July amid mass protests.
They also accused alliance leaders of failing to criticise police powers and military trials in the draft constitution, and failing to promote democratic and social demands.