The 31-year-old man was arrested after an investigation by police and Australia Post security personnel, the Australian Broadcasting Corp. reported Wednesday.
The postal worker, whose name has not been released, is accused of failing to deliver two gift cards in September and using them at a Sydney store, ABC said.
Police say he had four stolen gift cards in his wallet when he was arrested, and a search of his home found 161 cards and gift vouchers, and merchandise bought with the stolen cards.
Scott McIntyre, spokesman for the Australia Post, said they would not tolerate theft and would continue to fight it.
"We're angry and outraged that a staff member would be involved in something like this," McIntyre said. "It's an isolated incident which reflects negatively on our 35,000 other hardworking staff who are honest."
The alleged thief has been released on bail and will face trial on charges of mail theft and obtaining money by deception, ABC said.