Abstract Spin polarization of two-dimensional electron gas (2DEG) at the interface of EuTiO3/STO heterostructures has been theoretical predicted and experimentally observed via X-ray magnetic circular dichroism and polarized X-ray absorption spectroscopy, which, however, is lack of magnetotransport evidence. Here, we report the fabrication of high-quality EuTiO3/STO heterostructures by depositing antiferromagnetic insulating EuTiO3 thin films onto STO substrates. Shubnikov-de Haas oscillation, Hall, and magnetoresistance (MR) measurements show that the interface is not only highly conducting, with electron mobility up to 5.5×10^3 cm2V-1s-1 at 1.8 K, but also shows low-field hysteretic MR effects. MR of 9% is observed at 1.8 K and 20 Oe, which is one order of magnitude higher than those observed in other spin-polarized 2DEG oxide systems. Moreover, the heterostructures show ferromagnetic hysteresis loops. These results demonstrate that the high-mobility 2DEG is spin polarized, whose origin is attributed to the interfacial Ti3+-3d states due to oxygen deficiency and the exchange interaction between interfacial Eu spins and itinerant Ti-3d electrons.