Mladic had the surgery on Wednesday and called his family after the operation, B92 reported. His condition was not revealed.
"We do not release details about the indictee's health condition without his permission," U.N. tribunal spokeswoman Nerma Jelacic said.
He was hospitalized Tuesday, officials said.
The day Mladic was transferred to hospital, the prosecution asked the Tribunal to split the indictment against the former Republic of Srpska Army commander and conduct two trials, Serbian media reported.
Prosecutors told the International Tribunal for the Former Yugoslavia they wanted to try Mladic separately for crimes he allegedly committed in Srebrenica and for the siege of Sarajevo, the Tanjug news agency reported. They said they would try the Srebrenica crimes first and wanted to expand the indictment to include war crimes committed in the village of Bisina.
Among other things, the former military commander of Serbs in Bosnia is accused in the massacre of up to 8,000 Muslim men and boys in July 1995 in Srebrenica and the prolonged siege of Sarajevo. He was arrested in northern Serbia May 26.
Prosecutors said Mladic's arrest came as the mandate of the war crimes tribunal was about to expire. They argued that they wanted to go to trial as soon as possible because of the tribunal's mandate, concerns about the defendant's health and the desire to "maximize the prospect of justice for the victims," Tanjug said.