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Recycling high-grade rare earth polishing powder waste (REPPW) is crucial for protecting the environment and sustainable utilization of rare earth resources. Leaching REPPW in the eco-friendly H 2 O 2 -H 2 SO 4 suffers from the lack of understanding of the leaching mechanism. Here, the leaching mechanism was investigated under the optimal leaching conditions, i.e., T = 353 K, L/S ratio = 40 mL/g, H 2 SO 4 concentration = 4 mol/L and initial H 2 O 2 concentration = 0.8 mol/L, by which leaching efficiency of Ce and La reached 99.3% and 99.1%, respectively. Furthermore, pseudo steady state kinetic analysis suggested a five-step leaching mechanism involving CeO 2 hydroxylation, H 2 O 2 -CeO 2 coordination, ≡ Ce III − H 2 O 2 deprotonation, ≡ Ce IV − H O 2 − reduction and ≡ Ce III − H O 2 ∗ protonation, which was verified by the agreement between experimental data and the proposed reaction model. This work proposes a leaching mechanism of REPPW and would help develop an effective and sustainable recycling process for rare earth secondary resources. [Display omitted] • Ce and La were effectively leached from REPPW using the H 2 O 2 -H 2 SO 4 system, resulting in leaching efficiencies of 99.3% and 99.1% for Ce and La, respectively. • A reasonable leaching cycle of CeO 2 in the H 2 O 2 -H 2 SO 4 system was verified by a pseudo steady state analysis. • A clean and efficient method for recycling rare earth solid waste resources [ABSTRACT FROM AUTHOR]