High Court Judge Thokozile Masipa said Friday she was not persuaded there was a "reasonable prospect of success on appeal," after the state sought a longer jail sentence for the 29-year Paralympian.
She rejected prosecutor Gerrie Nel's argument that his six-year sentence is "shockingly lenient and disturbingly inappropriate."
Pistorius, a multiple gold winner, shot his girlfriend Reeva Steenkamp, a model and law graduate, in the early hours of Valentine's Day in 2013, saying he mistook her for a burglar.
He was initially sentenced for the lesser charge of culpable homicide, the equivalent of manslaughter. But last December, an appeals court upgraded his conviction to murder.
In July, he was sentenced for the new conviction to serve six years, less than half the minimum 15-year jail term for murder.
Longer sentence unnecessary
At his sentencing, Masipa, who presided over the lengthy trial, took into account the athlete's claim that he believed he was shooting an intruder.
"I'm of the view that a long term of imprisonment will not serve justice," Masipa said at the time.
But prosecutor Nel said in court Friday that Steenkamp had suffered a "horrendous death" and that Pistorius had never offered an acceptable explanation for having fired four shots through the toilet door. He had petitioned for a 15-year prison term.
Women's rights groups say Pistorius has received preferential treatment compared to non-whites and those without his wealth or celebrity status.
The prosecution now has the option of petitioning the Supreme Court of Appeal to request the sentence to be toughened.
Pistorius pleaded not guilty at his high-profile trial, saying he was trying to protect her, and not kill her in anger after a fight.
Earlier this month, local media reported that Pistorius had been put on suicide watch following mysterious wrist injuries.
Pistorius was not present at Friday's hearing.
mm/mg (AFP, AP, Reuters)