Abstract: Sr-Nd-Hf-Pb isotope data are important tools for tracing the mantle sources and decoding the petrogenesis of oceanic basalts, and thus it is crucial to obtain the real Sr-Nd-Hf-Pb isotopic compositions of altered oceanic basalts. Seawater alteration can modify the isotopic compositions of oceanic basalts, and acid-leaching prior to sample dissolution can efficiently reduce or remove the influence of seawater alteration. Most acid-leaching protocols focused on whether they can efficiently eliminate the effect of seawater alteration on Sr-Nd-Hf-Pb isotopes of young oceanic basalts. However, for ancient, highly altered oceanic basalts, prolonged interaction with seawater may have led to more complex alteration processes. It remains unclear whether the leaching protocols applied to young oceanic basalts can sufficiently remove the effects of seawater alteration on Sr-Nd-Hf-Pb isotopes of ancient altered oceanic basalts. Furthermore, when applying age correction to these isotopic values, whether to use the parent-daughter element ratios of unleached or leached samples requires further investigation. This study applied three acid-leaching procedures to basalts from the Lamont (81.6-87.1 Ma) and Caiwei (91.3 Ma) seamounts in the Western Pacific. The leached samples were analyzed for trace element and Sr-Nd-Hf-Pb isotope data. The results show that all leached samples have different Sr and Pb isotopic values from the unleached samples, but similar Nd and Hf isotopic values, indicating that seawater alteration have a great effect on Sr and Pb but negligible effect on Nd and Hf isotopic compositions. The four samples treated with procedure 1 (ultrasonically leaching 8-10 times with 6 mol/L HCl at 60 ℃) and procedure 3 (sequential leaching on an electric hotplate at 60 ℃ with 2 mol/L HCl for 2 h, 6 mol/L HCl for 2 h, 4 mol/L HNO₃ for 2 h, and 6 mol/L HCl for 12 h)—have similar Sr-Nd-Hf-Pb isotopic ratios (except for sample MASD65-1 showing slightly different Pb isotopic ratios). Comparing to procedures 1 and 3, two samples from Caiwei guyot treated with procedure 2 (leaching with 6 mol/L hot (60 ℃) HCl for 12 hours) have lower Pb isotopic ratios, indicating that procedure 2 did not efficiently remove seawater alteration effect on these two samples. Since seawater alteration can modify Rb, U, and Pb concentrations in oceanic basalts, the Rb/Sr, U/Pb, and Th/Pb ratios of unleached samples cannot represent their original compositions. When using the Rb/Sr, U/Pb, and Th/Pb ratios of both unleached and leached Lamont and Caiwei seamount samples to perform age corrections on the Sr and Pb isotopes of the leached samples, the correction results in significant deviations in the initial Sr-Pb isotopic values, whereas it does not change the initial Nd-Hf isotopic values. Furthermore, we found that for altered oceanic basalts older than 5 Ma, in order to obtain the accurate initial Sr-Nd-Pb isotopic values, it is necessary to analyze the Rb/Sr, Sm/Nd, U/Pb, and Th/Pb ratios from the same acid-leached aliquot and use the parent/daughter element ratios to perform age corrections on the Sr-Nd-Pb isotopes of the leached samples. Hf isotopic data do not require this correction. Considering the efficiency differences among the three acid-leaching protocols, this study recommends the use of procedure 1 or procedure 3 for processing ancient (＞5 Ma) altered oceanic basalts. Subsequently, trace element and Sr-Nd-Pb isotopic data should be analyzed on the same leached aliquot, and the initial Sr-Nd-Pb isotope ratios should be age-corrected using the parent/daughter element ratios on the same leached aliquot.