Zircon U-Pb geochronology has been widely used for determining the age of geologic processes. However,for very ancient zircon samples (e.g., ~3.8 Ga), the quality of U-Pb dating results may be affected by the relatively high-grade ofPbloss caused by the crystal damage through radioactive decay of U and Th. Here, we present a comparative study to explore the effectof thermal annealing (TA) and chemical abrasion (CA) on zircon U-Pb geochronology using zircon samples from some of the oldestigneous rocks on Earth (the Acasta Gneiss and the Muzidian Gneiss complexes), with the goal of getting better constrained zirconU-Pb ages of ancient rocks. Prior to the laser ablation dating experiments, all zircon samples and reference standards were thermallyannealed (850 ℃ ~ 1050 ℃/48 h), and a subset of thermally annealed zircon samples was then selected for chemical abrasiontreatment (partial dissolution using hydrofluoric acid at 170 ℃ for12 h), in order to remove radiation damaged domains. The resultsshow that the U-Pb ages of CA zircon grains appear to be more concordant with smaller MSWDs than those of the TA and untreatedzircon grains, indicating that the partial dissolution treatment of thermally annealed zircon grains effectively removed domains withPb loss, leaving the rest of the zircon crystal lattice relatively unaffected. Therefore, for complex and ancient (> 3.8 Ga) zirconsamples, chemical abrasion prior to laser ablationis shown to be useful for reducing Pb loss and datascatter. Thermal annealing appears to improve thematrix match between the unknown and referencezircon grains, which is especially useful for thedating of high U, young zircon samples.Additionally, our results show no systematicdifference in the trace elements and Hf isotopiccompositions between treated and untreated zirconsamples, which demonstrates that the treatmentsdo not have negative effect on the trace elementsand Lu-Hf isotopic compositions in zircons.