Joyce Mujuru and Joseph Msika were sworn in at State House in Harare.
"The two vice-presidents were sworn in this morning because their positions are not in dispute," a senior government spokesman told Reuters news agency.
Nelson Chamisa, spokesman for Movement for Democratic Change (MDC), which signed the power-sharing deal, said that the swearing-in of the two vice-presidents was "meaningless".
"Whatever appointments or acts that do not address the woes of the country are meaningless," he said.
"Any appointments by Mr Mugabe that do not take the country out of the current economic quagmire are meaningless."
Mugabe's governing Zanu-PF has taken 14 key positions including the defence and interior portfolios. It also controls the all-important state run media.
The MDC has been allocated 13 ministries, among them constitutional and parliamentary affairs, economic planning and investment promotion, labour and social welfare, sport, arts and culture, and science and technology development.
Morgan Tsvangirai, the leader of the MDC, on Sunday threatened to pull out of the September agreement.
"That is not power sharing, it is power grabbing," he told a rally in Harare on Sunday.
"The people have suffered. But if it means suffering more in order for them to get what is at stake, then so be it."
The European Union, meanwhile, said on Monday that it could step up sanctions on Zimbabwe unless Mugabe adheres to the terms of accord.
"If the agreement is not applied we shall resume our sanctions and reinforce them," Bernard Kouchner, France's foreign minister, said.