Michael Linley was arrested at Perth International Airport in October. Customs officers found 217 frogs, lizards and snakes in his suitcases.
Linley was fined A$10,000 (£4,000) and could face a much bigger fine when he's sentenced on a more serious charge on Monday.
He said he thought the animals would have a better chance of staying alive if he took them home to the UK.
Linley was worried that the animals would be killed on Australia's outback roads, so tried to take them out of the country, which is against the law.
Linley has worked for nature magazine National Geographic and has written a number of books about amphibians.
Other people have more criminal reasons for taking animals out of Australia, because some of them are worth thousands of pounds in other countries.
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