Ahmed was expected to lose more weight in the coming months, a spokesperson told the BBC.
Eman Ahmed, after her first laparoscopic sleeve gastrectomy surgery, is able to sit. "She had an uneventful surgery and anaesthesia course", a hospital medical bulletin said on Thursday.
A spokeswoman for Dr Muffazal Lakdawala, who is leading Abd El Aty's treatment, said the 37-year-old Egyptian's weight had been brought under 400 kilograms (881 pounds) since she arrived in Mumbai in early February.
Doctors plan to make Eman lose at least 100 more kilos (200 kg in total) over the next 6 months and are surprised at the rapid rate with which the patient is shedding pounds.
Eman is in Mumbai with her sister Shaimaa Ahmed who has a toddler back in Alexandria to take care of.
Last month, world's heaviest women in the world from Egypt arrived at the India's biggest city Mumbai for her bariatric surgery.
"We are happy to inform all well-wishers that the medical team of Saifee Hospital has successfully performed the surgery on Eman Ahmed", said a statement.
"Eman has lost more than 100 kilograms and her weight is gradually decreasing every day through medical treatment and follow-up", she told AFP.
Her family told the doctor that as a child she was diagnosed with elephantiasis, a condition that causes the limbs and other body parts to swell, leaving her nearly immobile. She also faced some other serious ailments including diabetes, high blood pressure, hypertension and sleep deprivation due owing to the problem of heavy weight.
In December 2016, Indian Foreign Minister Sushma Swaraj helped her obtain a visa to India, where a team of dedicated local doctors are supervising her case.
Abd El Aty was transported on a mini-truck to the airport, where she was flown on a chartered plane to India.
Bariatric surgery is a procedure that reduces weight loss by restricting the intake of food the stomach can retain.