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This study was performed to examine theeffect of different concentrations of an essential oil mixture (EOM) added todrinking water on growth performance, internal and external egg quality, andegg yolk fatty acid composition in laying hens. A total of 240 Brown Nicklaying hens aged 20 weeks were used in this study. These hens were divided intoone control and three treatment groups whose drinking water was supplementedwith 0, 0.1, 0.2, and 0.3 ml/L of Oregofarm EOM. Oregofarm is a commerciallyavailable product containing peppermint, oregano, and anise oil. Each treatmentgroup was further categorized into 10 subgroups, each consisting of 6 layinghens. The hens were fed basal rations for 16 weeks. For data collection andanalysis, a 16-week period was divided into three time periods of 5 weeks. Theweights of 25- to 30- and 35-week eggs were recorded weekly. In the groupswhose drinking water was supplemented with the EOM, there was a significantimprovement in egg production (EP) (p<0.001), weekly egg weights during theentire study period (p<0.001), and feed conversion ratio (p<0.05).Furthermore, egg shell thickness and yolk height were significantly increased(p<0.05) at week 35. The Haugh unit was also significantly improved(p<0.05) at weeks 25 and 30. However, feed intake and body weight were notaffected by the treatment (p>0.05). The levels of saturated fatty acids weredecreased, whereas the levels of polyunsaturated fatty acids increased with EOMsupplementation, although the differences were not statistically significant(p>0.05). Therefore, based on the beneficial effects of supplementing drinkingwater with different concentrations of EOM on egg weight, egg production, feedconversion ratio, and egg yolk fatty acid compositions, it is suggested thatEOM can be safely added at concentrations of up to 0.3 ml/L (i.e., the levelsused in this study) to drinking water for laying hens.