Archaeosynthemis occidentalis is a species of dragonfly of the family Synthemistidae, known as the western brown tigertail. It is a medium-sized dragonfly with reddish-brown and yellow markings. It is endemic to south-western Australia where it inhabits boggy creeks and swamps.

Archaeosynthemis occidentalis appears similar to Archaeosynthemis orientalis found in eastern Australia.

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