<p>Clinopyroxene (Cpx), a common mineral in basalt, has become increasingly important in elucidating mantle source and magmatic processes. Basalts collected from Pohnpei Island, a site of hotspot activity linked to the Caroline mantle plume, are rich in Cpx phenocrysts, of which some exhibit zoning textures. This study presents the in situ major and trace element compositions, as well as the Sr isotope ratios, of Cpx phenocrysts in Pohnpei basalts. The Cpx crystals in samples DS1 and DS2 exhibit core-rim zoning, characterized by a large and homogeneous core and a slightly brighter, very thin rim. The Cpx crystals in samples S7 and S8 display complex core-mantle-rim zoning. The dark domains of these Cpx crystals have higher Mg^# values but lower FeO and TiO₂ contents than the bright domains. The zoned Cpx crystals in S7 and S8 basalts display larger compositional variations than those in DS1 and DS2. Notably, the Cpx zones in four samples (S7, S8, DS1, and DS2) exhibit similar rare earth element (REE) distribution patterns and ⁸⁷Sr/⁸⁶Sr values (0.703 426–0.704 622), suggesting a common or similar mantle source. We suggest that the Cpx crystals in the Pohnpei basalts crystallized from multiple batches of heterogeneous mixing magma that were derived from an EM II-like end-member and mixed with Pacific-type depleted mantle components. The zoning textures and compositional variations recorded in these Cpx crystals provide insights into complex magma chamber processes, including fractional crystallization (involving olivine, Cpx, and Fe-Ti oxide) and magma mixing. Pressure-temperature calculations using the Cpx-only thermometer and barometer indicated that the Cpx crystals in DS1, DS2, S7, and S8 crystallized within the lower crust under similar temperatures and pressures. This study contributes to a comprehensive understanding of mantle source compositions, magmatic processes, and the complex mixing within magma chambers beneath Pohnpei Island.</p>