A preparation of essential oils to control chicken lice (Menopon gallinae) and mites (Ornithonyssus bursa) was developed. Each essential oil was effective against lice and mite in vitro. Citronella oil at the lowest concentration of 0.208 µg/cm2 resulted in a mortality rate of 100% in chicken lice, whereas a higher concentration of cloves, lemongrass, ginger, Makwan oil (0.416 µg/cm2), and Litsea oil (0.832 µg/cm2) was also found to be effective. A 100% rate of mortality for mites was observed using citronella and ginger oil at a concentration of 0.416 µg/cm2. At the same concentration, cloves, lemongrass, Litsea, and Makwan oil exhibited mortality rates in mites of 77.96%, 93.33%, 87.30%, and 93.49%, respectively. The efficacy of citronella oil and ginger oil against lice and mites was further examined in vivo. Citronella and ginger oil affected the rate of decline in lice from day 1 to day 14, whereas the number of mites living in nests declined from day 1 to day 7. The reduction of these parasitic insects may be correlated with the chemical constituents present in each essential oil. The active ingredients likely acted insecticidal agents against both parasitic insects. Moreover, the preparation developed here did not cause any side effects, such as dermatitis and respiratory disorders, during animal trials. Hence, preparations comprised of the essential oils of citronella and ginger can be further developed and used as insecticidal agents to control and/or eliminate chicken lice and mites on commercial farms.