The Maoists, who had fought a 10-year insurgency against the government in which an estimated 13,000 people died, agreed to rejoin the interim coalition government last week.
The reconciliation came only after the seven main political parties agreed to abolish the country's monarchy immediately after elections now scheduled for April.
The Maoists had withdrawn their political involvement in September demanding electoral reform and the removal of the king.
The government then postponed elections which had been planned for November.
Four of the five cabinet ministers had already served in the government between April and September. The fourth member, Matrika Yadav, will be minister for forest and soil conservation.
Pampha Bhusal is the only one new to the cabinet, and will be the minister for women and social welfare.
Yami said: "As a responsible party representing the people, we will do all we can to work for the nation and the people and for sustainable peace."
The communist group gave up its armed revolt last year .