Ten RAPD primers and two isozymes were used to determine genetic biodiversity for thirteen genotypes representing six different species of Solanum (S. villosum, S. nigrum, S. incanum, S. glabratum, S. torvum, and S. dulcamara). The plant samples were collected from different five areas in Aseer province, south-west of Saudi Arabia. We aim, fill in some of the present gaps in the Solanum species taxonomy in Saudi Arabia. The RAPD used primers amplified 159 bands, 143 of them were polymorphic (89.94%). Alcohol dehydrogenase isozyme showed a low level of variation with four polymorphic enzymatic bands. While, malate dehydrogenase isozyme showed a relatively higher level of polymorphism in which ten polymorphic out of total twelve enzymatic bands were scored. Our results indicated that S. nigrum and S. villosum can be divided into two or three subspecies. We suggest that S. nigrum was originated from S. villosum. Solanum torvum may be related to S. nigrum. Solanum incanum had different genetic origin from the other species under study. We decided some specific markers for Solanum species and genotypes.