Reddy, who had quit the Lok Sabha as a Congress member, was re-elected from Nellore in Andhra Pradesh as a candidate of the YSR Congress.
Reddy took oath as member in Telugu and in the name of God.
Dimple Yadav, who won unopposed the bye-election to Kannauj seat in Uttar Pradesh, took oath in Hindi and in the name of God.
Yadav was elected to the Lok Sabha from a seat vacated by her husband Akhilesh Yadav after he was sworn in as Uttar Pradesh Chief Minister.