BACKGROUND: The medicinal plant of Thymus serpyllum L. in nature, depending on the geographical region, climatic conditions, and growing environment, is represented with some chemotypes. Composition and quantitative content of the basic groups of the biologically active substances can be differed, and thus their biological properties are also various. AIM: The aim of the study was to determine possibility of the using the ultrasonic extracts of two chemotypes of T. serpyllum L. of Central Kazakhstan as an antimicrobial agent against test strains of microorganisms. MATERIALS AND METHODS: Two samples of T. serpyllum were extracted with 70% ethanol using ultrasound. The polyphenol content of the ultrasound extracts was determined using the LC-ultraviolet-ESI- tandem mass spectrometry technique. A study of an antimicrobial activity of the ultrasonic extracts was performed with eight strains of Gram-positive bacteria, six strains of Gram-negative bacteria, and four cultures of fungi. RESULTS: The ultrasonic extracts of two chemotypes of T. serpyllum L. are similar in composition of phenolic compounds but differ in a quantitative content of phenolic acids and flavonoids, except for a rosmarinic acid. The ultrasonic extracts have a wide spectrum of antimicrobial activity, exhibit the bactericidal or bacteriostatic activity against all tested bacteria and fungi at a concentration of 0.0625–20 mg/ml, but differ in their strength of action against test strains of microorganisms. CONCLUSION: The ultrasonic extracts of two chemotypes of T. serpyllum L. of Central Kazakhstan can be considered as a potential drug with a wide spectrum of antimicrobial activity. The results of chromatographic analysis will be used for standardization of a drug.