Selenium/carbon-rich (Se/carbon-rich) core-shell composites are prepared by a one-step hydrothermal synthesis method as a cathode for rechargeable lithium batteries. The Se/carbon-rich composites are characterized and examined by X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetry (TGA) measurements. It is demonstrated from galvanostatic discharge/charge process that the Se/carbon-rich composites exhibit the discharge capacity of 558 mA h g-1 in the first cycle and maintain capacity of 181 mA h g-1 after 80 cycles at a rate of 0.5C, which is better than that of the pristine selenium. The result demonstrates that the unique core-shell structure is effective in suppressing the dissolution of polyselenides into the electrolyte and in maintaining high utilization of the active materials during the charge/discharge process. It provides a new selenium-based cathode material for rechargeable lithium batteries.