Two girls, aged 14 and 15 have been arrested on suspicion of wounding after the attack in Doncaster, which happened at 5.15pm today.
Police said tonight the girl was in a stable condition in hospital with injuries that are not believed to be life-threatening.
A spokesman for South Yorkshire Police said: "A 15 year-old girl is in a stable condition in hospital with injuries that are not believed to be life-threatening, following an incident in Doncaster today, Thursday 7 December.
"Officers were called to Jenkinson Grove at Armthorpe at 5.15pm, after the girl was found with what is believed to be a stab wound to her stomach.
"Enquiries are continuing after a scene was secured at a nearby park.
"Two girls from Doncaster, aged 14 and 15, have been arrested on suspicion of wounding.
Anyone with information about the attack is asked to ring police on 101 and quote incident number 712 of December 7.