In order to distinguish between different species and populations of Mentha, the root, shoot, petiole length, internodal distance as well as their morphological and karyological features were taken as principle parameters. In Mentha piperita L. population 1 the internodal distance of the shoots was little shorter (2.8±1.24 cm) than population 2 (3.5±0.72 cm). The internodal lengths were nearly equal in population 1 and population 2 of M. arvensis L. but were longer than population 3. Leaf area was smaller in population 3 of field mint than the other two populations. However, population 2 possessed the highest leaf area (15.02±0.36 cm²) among the five populations of two species studied. Flower color also varied from whitish to whitish lavender to pale purple in all the five populations. All these morphological characters clearly indicated variation among different species. The size of the chromosome varied between the species and populations with the difference in ploidy level. The genus Mentha regarded to be a polyploid group with x=12 as the basic chromosome number (Ruttle 1931). Among all the populations of these two species studied, population 1 of M. piperita L. contained larger chromosomes. The total chromosome length, mean chromosome length, total chromosome volume and mean chromosome volume differed among the populations. These investigations were undertaken to prepare a comparative morphological and chromosomal database within these five populations of two species of Mentha. All these data indicated that the five populations of Mentha differed in minute karyotypic details and each population contained different types of chromosomes in variable numbers, revealing uniqueness of individual populations of each species.