Abstract: Achillea millefolium (Yarrow) has been used as a spice and medicinal plant in many ancient cultures from olden times. Today, biochemical investigations have shown different bioactive components responsible to medicinal and therapeutic properties of yarrow, in particular antimicrobial effect of it. Aim of this study is in vitro assessment of potential of inhibitory function of alcoholic extract of Achillea. millefolium on some microorganisms and comparison antimicrobial activity of yarrow with some antibiotics from penicillin family. The plants were used in this investigation, collected from Urmia region. The alcoholic extract of aerial parts of Achillea millefolium has been tested for antimicrobial activity in a disk diffusion assay. Also, microorganisms were used in this examination were divided in 2 categories: Control (Staphylococcus aureus, Salmonella enteritidis, Escherichia coli) and clinical isolated microorganisms (Staphylococcus aureus, Sterptococos Pneumoniae, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Enterobacter aerogenes, Proteus mirabilis) and 2 fungi (Aspergillus niger and Candida albicans). According to results of this study, the most sensitive organism to extract of yarrow was Staphylococcus aureus (p<0.05). The antibacterial activity of the plant was lesser to Ampicillin and greater or similar to other penicillin derivatives. With attention to our finding and other related reports in this field, it could be concluded alcoholic extract of yarrow has considerable antimicrobial effect on control and wound pathogen microorganisms. In spite of it, before application of the extract as antimicrobial agent, it must be more evaluated in vivo and clinically.