This paper presents, for the first time, cytogenetic data of the six-eyeds sands spider Sicarius sp. (Araneae: Sicariidae), southern Perú, including some features of meiosis and sex chromosomes, comparing with Sicarius tropicus from Brazil and 5 species of Loxosceles. Testes were treated with KCl, hypotonic, fixation, and chromosome preparations were stained with Giemsa solution. Analysis showed 2n = 21 chromosomes metacentric, subtelocentric and telocentric in spermatogonial metaphases. (2n = 18 + X1, X2, Y). Metaphase I showed nine autosomal bivalents and three sex chromosomes, these data are compared using a phenetic analysis of karyotypes to assess differentiation and chromosomal evolution in this family.