Murray is set to be sentenced next Tuesday on an involuntary manslaughter conviction.
Murray's defense team argued testing would verify the accuracy of the prosecution's theory that Murray placed Jackson on an IV drip of propofol and the local anesthetic lidocaine before leaving the room.
The defense contends Jackson was never on an IV drip. If the bottle came back negative for lidocaine, the defense was going to file a motion for a new trial based on the new evidence.
Deputy District Attorney David Walgren contended there was no legal basis for the testing and said Murray received a fair trial.
Pastor examined the propofol vial, which was found in the closet of Jackson's bedroom, before issuing his ruling.
However, Superior Court Judge Michael Pastor rejected the request, saying the defense should have asked for testing before Murray's conviction.
"You're not involved in fishing, you're involved in foraging," Pastor said.
The Associated Press contributed to this story.