Gandhi who retained her turf Rae Bareli in the high-stake Lok Sabha elections, took her oath in Hindi.
While there was a loud thumping of desks by the Congress members, voices were heard from the BJP benches "greeting" Sonia Gandhi "for taking oath in Hindi", news agency PTI reported.
Her son and Congress President Rahul Gandhi appeared to be capturing the moment on his mobile phone from the opposition benches.
Rahul took oath as the Lok Sabha member on Monday in the afternoon.
Immediately after Gandhi, BJP MP and former minister Maneka Gandhi was administered the oath and she and her sister-in-law Sonia Gandhi greeted each other with folded hands.
Maneka Gandhi was elected from Sultanpur in Uttar Pradesh. Her son Varun Gandhi, who was elected from Pilibhit, also took oath.
Alphabetical order is followed for states in administering oath to their members.
The maiden session of 17th Lok Sabha commenced on Monday with Prime Minister Narendra Modi, Congress president Rahul Gandhi, Defence Minister Rajnath Singh, Home Minister Amit Shah and Transport and Highways minister Nitin Gadkari among the prominent members who took oath on the first day.