Increasing demand for higher energy efficiency calls for waste heat recovery technology. Thus, facilitating practical thermoelectric generation systems is strongly desired. One option is enhancing the thermoelectric power factor, S 2/r, where S is the Seebeck coefficient and r is the electrical resistivity, although it is still challenging because of the trade-off between S and r. We demonstrate that enhanced S 2/r can be achieved by incorporating magnetic interaction in ferromagnetic metals via the spin fluctuation arising from itinerant electrons. We show that electron-doped Heusler alloys exhibit weak ferromagnetism at T C near room temperature with a small magnetic moment. A pronounced enhancement around T C was observed, with a 20% improvement in the power factor from the case where spin fluctuation is suppressed by applying magnetic field. This result supports the merit of using spin fluctuation to further enhance thermoelectric properties and the potential to further probe correlations and synergy between magnetic and thermoelectric fields.