In this study, 20 basil genotypes-3 cultivars, 1 local and 16 from the United States Department of Agriculture (USDA) were cultivated under the same conditions to determine some phenotypic properties by using the International Union for the Protection of New Varieties of Plants (UPOV) criteria; isolated essential oils and ethanol extracts were subjected to detailed chemical analyses and their biological activities were tested. According to the analysis of the essential oils, most of the examined genotypes belong to the estragole-rich chemotype. In addition, the PI 197,442, PI 211,586, PI 531,396, PI 652,070, PI 652,071, PI 414,197, Ames29184 genotypes and dino, moonlight cultivars belong to the estragol/linalool chemotype. Also, the Bolu genotype belongs to the citral chemotype, while the PI 296,391 and PI 190,100 genotypes belong to the estragole/citral chemotype. Among the 20 basil genotypes tested, the PI 174,284, PI 190,100, PI 531,396 and PI 197,442 genotypes had the highest antioxidant activity compared with the other genotypes and cultivars. The PI 652,071, PI 190,100, PI 197,442 genotypes and dino cultivar were found superior with respect to phenolic and flavonoid amounts as compared with other genotypes and cultivars. Variation in the main components of essential oils of basil genotypes grown under the same ecological conditions was observed. Therefore, the results we obtained are important for the selection of components with the desired properties. Also, dendrogram, correlation and biplot analyses were conducted to obtain genetic differences. Generally, genotypes and cultivars are divided into two main and two subgroups. Group B included more than 50% genotypes or cultivars. Correlation and biplot analyses showed relationship, and the examined properties were found related with similar. Some UPOV criteria, such as UP-1, UP-3, UP-6 and UP-7, were found similar in all genotypes and cultivars. However, other UPOV criteria showed differences among the basil genotypes and cultivars. Therefore, the dendrogram analyses were carried out to determine the relationship among the genotypes and cultivars depending on UPOV criteria. The dendrogram analyses divided into two main groups and two subgroups. UP-4 and UP-14 properties were the main factors for the characterization of the groups. In addition, we found antioxidant activity results showing that most of the examined genotypes are a good source of natural antioxidants with potential application in the food and pharmaceutical industries.