The objective of this study is to examine separation of valeric acid from aqueous solutions using an imidazolium-based ionic liquid and tributyl phosphate (TBP). As an imidazolium-based hydrophobic ionic liquid, [HMIM][PF6] (1-hexyl-3-methylimidazolium hexafluorophosphate) was used. TBP is utilized as an extractant in ionic liquid. An experimental examination of reactive extraction and physical extraction was performed and compared with each other. The effects of different parameters on separation such as extractant (TBP) concentration in [HMIM][PF6] (0-1.00 mol L-1), valeric acid concentration (0.10-0.30 mol L-1) and temperature (25 degrees C-65 degrees C) were investigated. In order to appraise the characteristics of extraction operation, extraction efficiencies (E), distribution coefficients (D) and loading factors (Z) were calculated by using the experimental data. This extraction study has shown that TBP in ionic liquid [HMIM][PF6] is an efficient extractant for valeric acid separation and the extraction efficiency has increased considerably as compared with the physical extraction. It was obtained that 1 mol L-1 TBP in [HMIM][PF6] extracts more than 87% of valeric acid from water.