Ultrathin few-layer materials have attracted intensive research attention because of their distinctive and unique properties. Few-layer GeP (FL-GP) is potentially interesting for application in electronics and optoelectronics because of its appropriate band gap and good stability under ambient conditions. Nevertheless, it is a challenge to achieve ultrathin few-layer or single layer GeP from exfoliation of bulk crystals. Here, a lithiation-assisted chemical exfoliation technique is employed to achieve FL-GP, in which the interlayer spacing can be efficiently enlarged after a preliminary lithium ion intercalation, allowing the bulk crystal to be readily exfoliated in a following ultrasonication. As a result, ultrathin FL-GP is obtained. In a demonstration, the FL-GP/reduced graphene oxide (rGO) demonstrates remarkable sodium storage performance. The FL-GP with a two-dimensional structure shortens the ion transport pathways and alleviates the volume variation during sodiation. Meanwhile, the rGO in the composite improves the conductivity of the whole electrode. The as-prepared FL-GP/rGO electrode exhibits a high capacity of 504.2 mAh g−1 at 100 mA g−1, remarkable rate performance, and superior cycling stability in the half cells. FL-GP/rGO//Na3V2(PO4)3 full cells are also assembled and demonstrated satisfactory electrochemical performance, indicating potential application of the as-prepared anode materials.