Regarding the adaptation of bacteria, either because of justified or unjustified excessive use of antibiotics, the efficacy of these decreases and microorganisms are likely to be constantly adapting to new antimicrobial agents. Campylobacteriosis caused by Campylobacter jejuni can cause many problems. Due to the acquisition of antibiotic resistance in our thesis we wanted to check the antimicrobial activity of plant extracts from flowers, leaves and stems of Anaphalis margaritacea on the bacterial Campylobacter jejuni NCTC 11168 strain. We first prepared ethanol extract from flowers, leaves and stems of Anaphalis margaritacea and with UHPLC-PDA-ESI-MS determined the presence of various phenolic compounds in the extracts. Then we determined the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the ethanol extracts. MIC and MBC of ethanol extract from flowers and leaves was 500 µg/mL, while MIC and MBC of ethanol extract from stems was 1000 µg/mL. According to the results, we have checked the influence of the ethanol extracts on membrane efflux pumps of Campylobacter jejuni NCTC 11168 strain, where we used the sub-inhibitory concentrations corresponding to ½ and ¼ MIC. The results showed a better effect of the ethanol extract from the flowers in a concentration corresponding to ¼ MIC (125 µg/mL) and leaves in a concentrations of ½ and ¼ MIC (250 µg/mL and 125 µg/mL) on the membrane efflux pumps, as the ethanol extract from the stems in a concentrations of ½ and ¼ MIC (500 µg/mL in 250 µg/mL). At a concentration corresponding to ½ MIC (250 µg/mL) of the ethanol extract from flowers we conclude that the used sub-inhibitory concentration already inhibits the growth of a bacterial strain Campylobacter jejuni NCTC 11168.