Polyploidization is an important technique used in grape breeding to create new genetic resources and can be induced using some antimitotic agents, including colchicine. Plants with increased ploidy can gain better quality than their original diploids in some characteristics. In this study, which was carried out to obtain polyploid genotypes under in vivo conditions, the effects of six (1 g L–1, 2 g L–1, 3 g L–1, 4 g L–1, 5 g L–1, 6 g L-1) doses of colchicine were applied to the shoot tip meristem regions of the seedlings obtained from the seeds of grapevine cv. Ekşi Kara and cv. Trakya İlkeren, for three consecutive days and twice a day (at 08.30 and 18.00 h) were in-vestigated. The effects of mutagen were evaluated by following the treated seedlings’ morphological changes and comparing them with the ‘Kyoho’ (4x) by flow cytometry (FC) analysis. In surviving plants after treatment, stomatal characteristics differed to varying degrees from their original diploids, and stomatal density decreased inversely with the increase in stomatal size in polyploid genotypes. Among cv. Ekşi Kara seedlings, 1 tetraploid (5 g L–1), and cv. Trakya İlkeren seedlings, 1 mixoploid (2 g L–1), and 1 tetraploid (6 g L–1) genotypes were selected by stomatal characteristics, chloroplast numbers, and confirmed by FC analysis. It was determined that colchicine is an effective mutagen in the breeding of polyploid grapevine, and stomatal observations, chloroplast numbers, and FC analysis are useful methods for obtaining confirmed results in the selection of polyploid genotypes.