Reduced graphene oxide (rGO)-SnO2 nanocomposites have been successfully prepared by one-spot facile hydrothermal method. The nanostructures of the samples were analytically inspected and found that SnO2 are evenly anchored on the surface of rGO sheets. The presence of surface defects was identified by spectroscopic techniques. The EPR results confirmed the presence of singly charged oxygen vacancies on the surface of rGO-SnO2 nanocomposites and found to be accountable for its room temperature ferromagnetism. The ferromagnetic behavior (coercivity, saturation magnetization and remanent magnetization) of rGO-SnO2 nanocomposites is suppressed as compared to pure SnO2. The incorporation of rGO sheets notably reduces oxygen vacancies in SnO2 and alters the room temperature ferromagnetism in rGO-SnO2 nanocomposites.