IAAF has suspended Russia’s athletics federation, after an independent report found evidence of widespread doping.
The Russian Olympic Committee and 68 athletes appealed against that decision but after hearing evidence from both sides, Cas has ruled the ban can stand.
The International Olympic Committee is considering calls to ban all Russian competitors from the Olympic Games following a second report into state-sponsored doping.
“The Cas panel confirmed that the ROC is not entitled to nominate Russian track and field athletes to compete at the Rio 2016 Olympic Games considering that they are not eligible to participate under the IAAF competition rules,” a spokesman said.
The IAAF said it was “pleased Cas has supported its position”, saying the judgement had “created a level playing field for athletes”.
IAAF president, Lord Coe, added: “This is not a day for triumphant statements. I didn’t come into this sport to stop athletes from competing.
“Beyond Rio, the IAAF taskforce will continue to work with Russia to establish a clean safe environment for its athletes so that its federation and team can return to international recognition and competition.”