The aim of this work was to investigate the chemical composition, antibacterial activity of essential oil and chromosome numbers from Inula crithoides growing in Algeria. The Analysis of the essential oils of two populations of I. crithmoides by GC/MS led us to the identification of 39 terpene components. The average yield of the essential oil of the two samples is 0.13%. We noticed the abundance of monoterpene hydrocarbons for both populations. The major components are ρ-cymene (36.19-35.51%) and α-croweacin (25.61-20.13%) for Ziama and the Grand-phare respectively. The population of Grand-phare, is characterized by the presence of a high rate of limonene (12.37%). Our investigation allowed us to identify the chemotype to (ρ-cymene-α-croweacin). The antibacterial activity of essential oils of I. crithmoides conducted on four bacterial strains shows that this oil is moderately active against Staphylococcus aureus ATCC 27853. The karyological study of I. crithmoides, showed the presence a karyotype with diploid chromosome number 2n = 2x = 18, and a base number of x = 9.