This multicenter prospective cohort study (n=54 early AD patients) evaluated lecanemab's efficacy and plasma biomarker dynamics over 9 months. Following treatment, Aβ1-40 and Aβ1-42 increased while GFAP, p-tau181, and p-tau181/Aβ42 ratio decreased, with significant changes observable as early as 3 months. Cognitive function (MMSE, CDR-SB, ADAS-cog, ADCS-ADL) remained generally stable, though ADAS-cog worsened at 9 months. Lower baseline Aβ1-42 predicted greater cognitive decline at 9 months, but changes in plasma biomarkers did not significantly correlate with clinical outcomes, suggesting these markers may not serve as short-term surrogate endpoints for treatment response.