Zn stable isotope signatures have proved effective in tracking Zn sources in polluted environments, however, interactions between Zn in solution and in minerals in soils and sediments can lead to notable Zn isotope fractionation and affect Zn source identification. Therefore, it is important to understand Zn isotope fraction during its sorption onto soil minerals and the underlying mechanism. In this study, we quantify zinc isotope fractionation during its sorption onto Al oxide, by performing experiments under various pH and total Zn concentrations and measuring Zn isotope signature using Multicollector-Inductively Coupled Plasma Mass Spectrometer (MC-ICP-MS). Results showed a systematic enrichment in heavy Zn isotopes on the surface of Al oxide, with Δ⁶⁶Zn adsorbed-solution ranging from 0.50±0.16‰ at low pH (e.g., pH 6) and low concentration (e.g., 0.2 mM) to 0.10 ± 0.02‰ at high pH (e.g., pH7.5) and high concentration (e.g., 0.8 mM). These different magnitudes of Zn fractionation are related to structural differences between Zn sorption mechanism existing on the high pH (octahedrally coordinated Zn by oxygen atoms) and low pH (tetrahedrally coordinated Zn by oxygen atoms), as evidenced by Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. EXAFS analysis also suggest Zn-Al layered double hydroxide (LDH) formed at high pH and high concentration, the structure of which has a Zn-O bond distance of 2.06 Å. In contrast, at low pH or low concentration, results from EXAFS indicates Zn sorbed as an inner-sphere surface complex, with Zn-O interatomic distance being 1.99 Å. These two distinct mechanisms indicate that Zn isotope fractionation is dominantly controlled by the chemical composition of the solution (pH, concentration) and these factors should be considered when using Zn isotope to track pollution source.