In this study, chromosome numbers and structures of some Origanum L. taxa growing in Turkey were identified. Using the Image Analysis System, the complements of plant accessions belonging to eight sections, namely Amaracus (Gleditsch) Vogel, Anatolicon Benth., Brevifilamentum Ietsw., Longitubus Ietsw., Chilocalyx (Briq.) Ietsw., Majorana (Miller) Ietsw., Origanum, and Prolaticorolla Ietsw. were determined, by classification with the cytogenetic method. The chromosome number of all taxa except O. sipyleum L. (2n = 28) and O. rotundifolium Boiss. (2n = 28) is 2n = 30. In addition, the hybrids and their parental species have 2n = 30 chromosome numbers. Also, the smallest chromosome length is 0.32 mu m in O. sipyleum. The largest chromosome length is 2.02 mu m in O. minutiflorum O.Schwarz & P.H.Davis. The smallest total haploid length is 10.08 mu m in O. vulgare subsp. hirtum (Link) A.Terracc. and the largest value is 22.00 mu m in O. haussknechtii Boiss. The smallest mean length is 0.33 mu m in O. vulgare L. subsp. hirtum and O. saccatum P.H.Davis. The largest mean length is 0.74 mu m in O. sipyleum L. The chromosome numbers obtained in this study support the speciation of Origanum members via homoploid hybridization. Finally, the somatic chromosome numbers of 10 taxa (including 2 hybrids), chromosome measurements of 22 taxa (including 2 hybrids), and ideograms of 19 taxa (including 2 hybrids) were for the first time performed in this study.