The present study reports a significant combined antibacterial activity ofCichorium intybusL. (known asChicory) natural extract with cold atmospheric-pressure argon plasma treatment against multi-drug resistant (MDR) Gram-negative bacteria. To detect reactive species that are generated in the argon plasma, optical emission spectra were recorded. The molecular bands were allocated to the hydroxyl radicals (OH) and neutral nitrogen molecules (N2). Moreover, the atomic lines form the emitted spectra were determined to argon atoms (Ar) and the oxygen atoms (O), respectively. The results revealed thatChicoryextract treatment at a concentration of 0.043 g/ml reduced the metabolic activity ofP. aeruginosacells by 42%, while, a reduced metabolic activity of 50.6% was found forE. colibiofilms. Moreover, the combination ofChicoryextract with 3 min Ar-plasma introduced a synergistic effect, so that it exhibited a significantly reduced metabolic activity ofP. aeruginosato 84.1%, andE. coliones to 86.7%, respectively. The relationship between cell viability and membrane integrity ofP. aeruginosaandE. colibiofilms treated withChicoryextract and argon plasma jet were also analyzed by CLSM. It was found that after the combined treatment, a noticeable membrane disruption was formed. Besides, it was concluded thatE. colibiofilms showed a higher sensitivity to Ar-plasma thanP. aeruginosabiofilm at longer plasma exposure times. This study suggests that the anti-biofilm therapy based on a combined effect ofChicoryextract and cold argon plasma treatment can serve as a considerable green method for treatment of antimicrobial MDR bacteria.