Ruto, the most senior official yet tried by the court, and his co-accused, journalist Joshua arap Sang, 38, face three counts of murder, deportation and persecution after a wave of violence swept Kenya in 2007-08.
Ruto did not say anything as he entered the court, with a bodyguard pushing journalists out of the way.
Sang proclaimed his innocence to a crowd of waiting journalists as he walked up the steps of the court building.
“We are here and now God will see us through,” Sang said.
“I did not contribute to the violence in Kenya, but peace.”