The court's decision on Saturday means that the prosecutor must expedite the work of presenting an indictment. The prosecutor had wanted to extend the detention until February 6, but the judge deemed that "there was not sufficient grounds" for an extension.
This was the prosecutor's second attempt to have the detention period extended. A first attempt was also rejected by the court in Seoul.
Yoon was arrested in a large police operation on January 15 after refusing to appear before investigators and instead barricaded himself in the presidential palace.
Yoon, who has been impeached, is temporarily suspended from the presidential post. In addition to the criminal investigation, Yoon's future as president will also be addressed by the country's constitutional court.
The 64-year-old Yoon is accused, among other things, of attempting to carry out a coup.
South Korea's President Yoon Suk-Yeol introduced a state of emergency on the evening of December 3 to protect the country from "communist forces". This was done with reference to the opposition having completely paralyzed the government's work.
On the night of December 4, the parliament voted to repeal the war laws and the state of emergency was declared invalid.
Yoon Suk-Yeol was stripped of his presidential powers on December 14, when the parliament voted to put him on trial.
In addition to the impeachment process in the constitutional court, the anti-corruption unit and the police are conducting a joint criminal investigation against Yoon.
Yoon has been suspended from his office temporarily. On January 15, he was arrested at the presidential palace after a first attempt to arrest him on January 3 was stopped by security guards who physically blocked the police.
