NEW DELHI, Aug. 23 (Xinhua) -- India's former prime minister Manmohan Singh took the oath as a member of the Upper House of Parliament on Friday.

The oath was administered by Upper House (Rajya Sabha) Chairman M. Venkaiah Naidu.

Aged 86 years, he was elected unopposed from the western state of Rajasthan.

Singh returned to the Rajya Sabha after a brief gap since his retirement from the Upper House on June 14. He had earlier represented the northeast state of Assam in Rajya Sabha.

A Rajya Sabha member, having a term of six years, is elected by the elected representatives of a state assembly and also the members of parliament (MPs) of the Lower House Lok Sabha belonging to?the specific state.