Background: Indonesia has a great potential in the development of antimicrobials from plants because Indonesia's biodiversity is among the highest with 30.000 plant species. The teh-tehan plants (Acalypha siamensis Olive. ex Gage) is potential plant as a source of antimicrobial compounds. This research aims to determine the antimicrobial activity of the methanol extract of teh-tehan leaves and their fractions and to determine the class of compounds. Method: Teh-tehan leaves simplicia powder was extracted by maceration method with methanol solvent, whereas the fractionation was carried out using a vacuum chromatography liquid method. Teh-tehan leaves extract were tested against S.aureus, P.auruginosa and C.albicans, whereas the fractions were tested against S.aureus. Samples were tested by the disc diffusion method. Results: The methanol extract of teh-tehan leaves had weak antimicrobial activity against S.aureus bacteria, but did not have antimicrobial activity against P.aeruginosa and C.albicans. Extract with a concentration of 10% showed the best inhibition zone with an inhibition zone diameter of 10.81 mm ±0.85 against S.aureus and 8.58 mm ±0.27 against P.aeruginosa. The class of compounds contained in the methanol extract of teh-tehan leaves are flavonoids, alkaloids, steroids and polyphenols. Fractions from the methanol extract of teh-tehan leaves have antimicrobial activity against S.aureus. The three most active fractions are fraction 7; 8 and 9 with a concentration of 2.5% showed inhibition zone with an inhibition zone diameter of 14.60 mm ± 1.56; 11,86 ± 0,95 mm and 9,62 ± 0,88 mm. Fractions 7 and 8 were identified to contain a class of flavonoids, steroids and polyphenols, while fraction 9 contained a class of flavonoids and polyphenols. Conclusion: methanol extract of teh-tehan leaves had weak activity as antimicrobial against S.aureus bacteria. Fractions from the methanol extract of teh-tehan leaves have antimicrobial activity against S.aureus bacteria. Fractions of the methanol extract of teh-tehan leaves showed better inhibitory activity against the growth of S.aureus bacteria. The methanol extract of teh-tehan leaves contains compounds belonging to the class of flavonoids, alkaloids, steroids and polyphenols. The three most active fractions contain a class of flavonoids, steroids and polyphenols.