In this paper, we report a simple method based on assembling n-alkanoic acids on hierarchical structured copper toward preparing surfaces with tunable oil wetting performance in water. Surface wettability from superoleophobicity to superoleophilicity in water can be regulated through tuning the chain length of n-alkanoic acids. Importantly, even in strongly acid and basic water, such phenomena can still be observed. The cooperation between the hierarchical structures and the surface chemical composition variation is responsible for the controllability. Meanwhile, the tunable ability is universal and the controllability is suitable for various oils including silicon oil, n-hexane, and chloroform. Moreover, the method was also used on copper mesh substrates, and we reported the related application of selective oil/water separation. This paper provides a flexible strategy toward preparing surfaces with tunable oil wetting performances, which can also be suitable for other materials, and offers some fresh ideas in manipulating underwater oil wetting performances on surfaces.