This is a list of members of the Western Australian Legislative Assembly between the 1901 election and the 1904 election, together known as the Fourth Parliament.
The names of parliamentary groupings, which were not formalised parties, were established prior to the 1901 election, with Ministerialists being those sympathetic to former Premier John Forrest, and Oppositionists and Independents defined accordingly. With the exit of Forrest from state politics following his successful shift to the federal Division of Swan, the Ministerial group was defeated in the election and had no obvious choice of leader, but the Opposition, led by George Leake, did not have sufficient numbers to govern in its own right. The failure of the Morgans Ministry in December 1901 after less than a month in office and the unprecedented defeat of three of its Ministers in ministerial by-elections allowed an Opposition-led government with Labour support to govern until the 1904 election with a reasonable level of stability. Therefore, the "Opposition" were in government and the "Ministerial" group was in opposition for most of the period. Bolton and Mozley (1961) introduce the terminology "Forrest party" and "Leake party", but these were not used by either the press or the groupings themselves.