His resignation comes hours after Emeka Nwajiuba, minister of state for education, who is also a presidential aspirant quit.
Recall that President Muhammadu Buhari had at FEC meeting on Wednesday, directed all members of his cabinet with political ambitions to resign.
Onu Submitted his letter of resignation to the Secretary to the Government of the Federation, Boss Mustapha.
Some ministers affected are Ministers of Transportation, Rotimi Amaechi; Niger Delta, Godswill Akpabio; Labour and Employment, Chris Ngige, who are also in the presidential race on the platform of the All Progressive Congress (APC).
Others are Abubakar Malami, minister of justice; Minister of State Mines and Steel, Uche Ogar, who is running for governorship position in Abia State, the Minister of Women Affairs, Paulline Tallen, who declared her ambition to contest for the senatorial seat in Plateau State.