Introduction: Today the use of medicinal plants to improve the immune system function and against pathogenic bacteria has been considered.

Background and aim: In this study, the effect of methanol extract of the aerial parts of Agrimonia eupatoria on peripheral blood mononuclear cells (PBMC) and 12 pathogenic bacteria were investigated.

Material and Methods: The methanol extract of branches, stems, seeds and leaves of Agrimonia eupatoria were prepared and the effect of different concentrations of 50, 100, 500, 1000, 1500, 2000 and 2500μg/ml of the extract on proliferation of PBMC was evaluated by MTT assay. Also the effect of concentrations of 1, 2, 4, 5, 7 and 10mg/ml of the extract was tested on 12 pathogenic bacteria by disc method and on nutrient agar media.

Results: The methanol extract of the branch, stem and seed of Agrimonia eupatoria showed the most stimulatory effects on immune system and induced the proliferation of PBMCs up to 8 times. Methanol extract of Agrimonia eupatoria showed antibacterial effects against gram-positive bacteria and the most antibacterial effect was on Bacillus subtilis at a concentration of 4mg/ml and Staphylococcus aureus at concentration of 7mg/ml.  

Conclusion: The Agrimonia eupatoria methanol extract showed stimulatory effects on the immune system and also antibacterial properties against certain gram-positive pathogenic bacteria. These finding indicate that Agrimonia eupatoria can be considered to use for immunodeficiency patients and moreover to control some bacterial infections.