Having won the Tidy Town award in 2013, the coastal town at the Moore River mouth will compete against Bondi Beach and other finalists to be named Australia's cleanest beach.
The Guilderton Community Association has been the driving force behind the town's previous KAB successes.
President Gillian Lamont credited its high level of volunteerism and community passion for the estuary and coastline.
"We are very proud to be representing WA, however the fact that we are so small with such limited resources, and given who our competitors are, taking out the national title will be a huge challenge," she said.
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READ NOWInitiatives included in Guilderton's state entry were the construction of a timber stairway from the top gazebo to the ocean, as well as the north Guilderton coastal restoration project, created to help protect native vegetation.
Shire of Gingin president Michael Aspinall said the result showed what a small community could achieve when faced with the challenge of conserving their coastal environment.
KAB judges will visit Guilderton on June 19 and the national awards will be in Sydney on July 21.