西澳大利亚州（英语：Western Australia、WA），简称西澳洲、西澳，是澳大利亚联邦的一个州，位于澳大利亚西部，今划分为142个地方政府区域，幅员广达2,525,500平方公里，占全国总面积1/3，是面积最广大之州。由于内陆有三大沙漠区，而人口仅有211万，占全澳总人口的1/10。

西澳洲的首府及最大城市是珀斯（Perth）。该州采用UTC+8时区，与东亚大多数国家的时区相近。但西澳于2006年12月3日起，在夏季期间试行为期三年的夏令时间，尔后经州内公民投票而取消。

虽然西澳离东岸的主要地区较为遥远，然而由于滨临印度洋，与印度、印尼、新加坡、马来西亚、泰国等南亚及东南亚国家相当接近，因此州府亦可视为澳洲与东南亚、南亚、非洲、中东展开合作关系的桥头堡。

Western Australia (abbreviated as WA) is a state occupying the entire western third of Australia. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Southern Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east. Western Australia is Australia's largest state with a total land area of 2,529,875 square kilometres (976,790 sq mi), and the second-largest country subdivision in the world – however, a significant part of it is sparsely populated. The state has about 2.6 million inhabitants, around 11% of the national total. 92% of the population lives in the south-west corner of the state.