Opportunistic infections are common and in the cases of cancer patients, they are very harmful. Bacteria such as Staphylococcus aureus, Streptococcus pneumoniae, Salmonella typhi, Escherichia coli, Pseudomonas aeruginosa,Shigella dysenteriae, and Proteus mirabilis isolated from cancer and other immunosuppressed patients were tested for their sensitivity to compounds of essential oils such as Citral, Limonene, Menthone and Thymol. In agar well diffusion method the selected essential oils were effective against both gram positive as well as gram negative organisms. For e.g, Citral was highly active against S.pneumoniae and least against S. aureus. Limonene was highly active against S.typhi and least against S. aureus. Menthone was highly active against P.mirabilis and least against P.aeruginosa. The results for Thymol were moderate, when compared with the reference drug ciprofloxacin. The results for minimal bactericidal concentration (MBC) were similar to minimal inhibitory concentration (MIC) results. As no organism was found to be resistant to the tested essential oil compounds, the results indicated that they could be used in different forms for the prevention, control and treatment of opportunistic bacterial infections caused by those organisms, particularly in cancer patients.