Since its invention, recombinant protein expression has greatly facilitated our understanding of various cellular processes in different biological systems because theoretically this technique renders any gene to be expressed in a mesophilic host like Escherichia coli, thus allowing functional characterizations of proteins of interest. However, such a practice has only yielded a limited success for proteins encoded in thermophilic archaea since thermophilic proteins are often present in an insoluble form when expressed in E. coli. As a result, it is advantageous to express recombinant proteins of thermophilic archaea in a homologous host, allowing a native form of recombinant protein to be purified and characterized. Here we present a detailed protocol for the homologous expression and purification of proteins in the thermophilic archaeon, Sulfolobus islandicus Rey15A.