Manuka oil named New Zealand’s tea tree oil is oil-soluble and comes firom nature. Manuka oil and its extract $alpha$-pinene, Oxy’less clear, R-limonene which is one of the component of Citron extracted from Grapefruit seed and Citrex were used to estimate the antimicrobial activity and to improve the capability of antiseptic. Disk diffusion method was used to measure the antimicrobial activity. Escherichia coli which is gram-negative bacteria and Staphylococcus aureus which is gram-positive bacteria were used as strain. The antimicrobial activity of Manuka oil and $alpha$-pinene for Escherichia coli, Staphylococcus aureus was similar when the concentration of Manuka oil and $alpha$-pinene are 10u/paper disk. However, antimi-crobial activity of Manuka oil fDr Escherichia coli, Staphylococcus aurem was better than that of $alpha$-pinene when the concentration of Manuka oil and $alpha$-pinene was low. Antimicrobial activity of Oxy’less clear is better than that of propyl para hydroxybenzoate(PPHB), R-limonene at all the concentration and is similar to that of $alpha$-pinene. Antimicrobial activity