The results of an investigation (floristic determination, chromosome number and the composition of the essential oil) of a mint-population, growing at Oudemolen (Dr.) have been rendered. According to a morphological determination and the composition of the essential oil it proved to be a hybrid between Mentha longifolia (L.) Hudson and Mentha suaveolens Ehrh. that is Mentha X niliaca Juss. ex Jacq. The seedlings of the hybrid did not differ from the original population concerning their habit and the composition of the essential oil, of which piperitone oxide is the main constituent. Chromosome countings gave for the population found 2n = 24; the same number as often found for Mentha longifolia and for Mentha suaveolens. From these data we voted for the hybrid form of Mentha X niliaca Juss.ex Jacq. with a gene composition of cc aa PP rr.