The unanimous decision by a three-judge Superior Court panel came barely two weeks after they heard oral arguments by Sandusky's lawyer and a state prosecutor.
Sandusky, who was convicted of sexually abusing 10 boys, had argued his trial lawyers did not have enough time to prepare the case and that the judge mishandled some jury instructions.
Sandusky had wanted the trial judge, John Cleland, to give jurors an instruction about the amount of time it took for nearly all of the victims to report their allegations. Judge Jack Panella, who wrote the opinion for the panel, said Cleland should have evaluated the need for such a jury instruction, but his failure to do so did not harm Sandusky.
As for Sandusky's claim that his lawyers did not have enough time to prepare for the case, Panella said trial judges have discretion about whether to allow pretrial delays, and that in Sandusky's case the judge carefully considered the continuance requests.
The 69-year-old is serving a 30-to 60-year prison sentence in Southwestern Pennsylvania. He is likely to die behind bars if his convictions are not overturned.
Defense lawyer Norris Gelman said he planned to ask the state Supreme Court to review the case.
The Associated Press contributed to this report.