A study about the antimicrobial activity test of black tea ethanol extract (Camellia sinensis) against Pseudomonas aeruginosa has been carried out. The black tea leaves are sourced from Sidamanik Plantation, North Sumatra. The dried black tea leaf extract was obtained by maceration technique in which black tea leaves were macerated for 24 hours. Then, the macerate was concentrated to obtain a thick extract and make sure that the ethanol had evaporated. After that, the concentrated extract was

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... de with a variation of 5%, 10% and 15%. The antimicrobial activity test used was the disc method, where distilled water was used as a negative blank. The results obtained for average SD for blank with diameter 6 mm, 5%, 10% and 15% extracts were 6 ± 0,00; 7,75 ± 0,35; 9,05 ± 0,07 and 9,95 ± 0,07 mm with the inhibition diameter 0 mm; 1,75 ± 0,35; 2,05 ±0,07 and 3,95 ± 0,07 mm. The conclusion of this study is that the concentration of the extract is straightly proportional to its inhibitory power, namely the higher the concentration of black tea ethanol extract, the higher its inhibitory activity against Pseudomonas aeruginosa, so it can be used as an antibacterial agent for Pseudomonas aeruginosa.