Zinhle Maditla, who was accused of killing her four children in Klarinet, eMalahleni, Mpumalanga was on Monday found guilty of premeditated murder.
Maditla was convicted in the Mpumalanga High Court sitting in Middelburg, National Prosecuting Authority regional spokesperson Monica Nyuswa said.
"She pleaded guilty and tomorrow [Tuesday] it will be arguments for sentencing," Nyuswa said.
Maditla had said in her plea agreement that she had taken some of the rat poison she gave to her children and asked the court for mercy, according to eNCA.
She was arrested on December 30, 2018, after she handed herself over to the Vosman police station.
This was shortly after the decomposed bodies of her four children - two girls aged four and eight, and two boys aged seven and 11 months - were found in her rented room.
Police spokesperson Brigadier Leonard Hlathi had earlier said that everything "seemed well at the time" that Maditla and her children were last seen on December 26.