The MnCO3-RGO composite, constructed by MnCO3 microcrystals in-situ nucleated and grown on reduced graphene oxide (RGO) sheets, are synthesized via a facile one-pot solvothermal process. When the MnCO3-RGO composite is used as anode material, it delivers outstanding electrochemical performance: it exhibits a large capacity of 873 mAh g−1 even after 400 cycles at a current rate of 1 C, which is over 55.6% higher than that of bare MnCO3 (561 mAh g−1); most importantly, the MnCO3-RGO composite demonstrates a superior high-rate performance and long-term stability with a very large capacity of 546 mAh g−1 even after 1000 cycles at a very large current rate of 5 C. This terrific electrochemical performance of MnCO3-RGO composite is mainly ascribed to its unique architecture: the excellent mechanical flexibility of RGO sheets can stabilize the microstructure of MnCO3 and guarantee the long-term stability during charge/discharge even at large current rate; the high conductivity of RGO sheets can effectively accelerate the transfer of electrons. This work presents a facile and cost-effective synthesis strategy, which gives a guidance for the synthesis of the other transition metal oxides-RGO composite.