A vital factor influencing shale oil exploration in lacustrine shale reservoirs is oil mobility, which is closely associated with the shale pore structure and fluid properties, especially for the low-maturity lacustrine shale in China. In this study, the oil mobility and shale oil potential in the Middle Eocene Shahejie Formation lacustrine shale (MES shale) of the Nanpu Sag in the Bohai Bay Basin were evaluated by using nuclear magnetic resonance (NMR) experiments. The low-maturity MES shale has low porosity with various pore types including intergranular and dissolution pores and microcracks. Its pore space spans nano- to microscale with dominant mesopores. The portion promoting fluid flow is complex and has good self-similarity with high high fractal dimensions. The porosity is related to the thermal maturity, and a higher maturity facilitates pore space development. The oil saturation in low-maturity shale is lesser with low free hydrocarbon due to the low the maturity. Considering the high viscosity and the dead oil, the NMR relaxation mechanism in smaller pore space of low-maturity shale is proposed to bulk relaxation. The movable oil with a viscosity lower than 10 cp accounts consideble pore space in the MES shale. Its viscosity relates with TOC content and thermal maturity. Comparing with other shale oil producing areas, MES shale has similar geological conditions and good brittleness, which hints a suitable and promising shale oil potential at low tectonic position in the Nanpu Sag under the technologies of in situ conversion process and hydraulic fracturing.