We have developed an effective protocol for in vitro micropropagation in order to obtain large numbers of identical plants and another protocol for in vitro polyploidization of Ajuga reptans, based on the use of oryzalin. Two donor plants of A. reptans (AR 4, AR 7) were treated with 0, 1, 5, 10 μM oryzalin for 2 weeks. The analysis of the ploidy level of these plants was verified by flow cytometric analysis using the internal standardization method. The effects of polyploidization on growth as well as morphological and stomatal size were also measured. After in vitro polyploidization, some plants became tetraploids or octoploids. The most efficient conditions for inducing tetraploidy were the treatments with 10 μM oryzalin.