A reduced graphene oxide/β-Ni(OH)2 composite with excellent supercapacitive performance was prepared by a facile chemical precipitation. Reduced graphene oxide was ultrasonically dispersed in a Ni(NO3)2 solution, forming a suspension. Then let the prepared suspension stand for 0.5h and 24h, respectively, followed by stirring and adding NaOH solution into it for obtaining two types of composites. It was found that the standing time notably affected morphology and supercapacitive performance of the resulting composites. The composite derived from the 24h-standing suspension presented an ideal morphology with nano-sized β-Ni(OH)2 particles homogeneously growing on the reduced graphene oxide sheets. The composite exhibited ultra-large specific capacitance, high rate capability and good cycling stability in 6molL−1 KOH electrolyte. Its maximum specific capacitance was 2134Fg−1 at a scan rate of 2mVs−1, and a large specific capacitance of 882Fg−1 was still preserved at a high scan rate of 70mVs−1. After 2000 cycles at a current density of 10Ag−1, the composite delivered a specific capacitance of 1141Fg−1, retaining about 81% of its initial capacitance. The high performance and the simple synthesis route allowed the obtained composite to be promising for supercapacitor applications.