A new species of Mouse Spider (family Actinopodidae Simon, 1892), Missulena harewoodi, is described from near the City of Kalgoorlie-Boulder in the Goldfields region of Western Australia. It differs from all other Missulena species by the unusual light grey colouration of the abdomen in combination with small body size and shiny carapace. A phylogenetic analysis of a fragment (658 bp) of the COI barcoding gene places M. harewoodi sp. n. in a clade with four Missulena species from the Pilbara region of Western Australia, more than 900 km away. Missulena harewoodi sp. n. is one of the many species in this genus that are currently only known from a single, or a very limited number of specimen, highlighting the paucity of fauna collections in many arid regions of Australia and the difficulties in sampling these cryptic spiders.