Continuous dendrites growth, as well as corrosion and side reactions of Zn metal anode seriously hinder the development of aqueous zinc ion batteries. To address these issues, oleic acid (OA) is dispersed into a 2 M ZnSO4 solution to form a novel colloidal Zn-ion electrolyte. The non-soluble OA surfactant doesn't coordinate with Zn2+ and the water solvent. Instead, it works as a 'temporary electrolyte additive'' during initial stage of battery processing. After, the OA additive is bonded to Zn metal forming an OA adsorption layer on the anode surface. This hydrophobic OA adsorption layer can not only regulate Zn deposition with parallel orientation of the Zn (0 0 2) plane to the Zn foil substrate leading to a flat Zn metal anode, but also isolate direct contact of water with Zn thus inhibiting the harmful side reactions on the Zn anode. Consequently, this colloidal electrolyte enables highly reversible Zn deposition with Coulombic efficiency of 99.63 % and cycle life over 3340 cycles. This strategy of in-situ facet engineering and interface modification of Zn metal anode using colloidal electrolyte presents a new perspective toward design of high-performance aqueous zinc ion batteries.