Lignin, a renewable resource, has been used as carbon precursor to prepare porous carbon nanofiber films by electrospinning with PVP as spinning agent and Mg(NO3)(2)center dot 6H(2)O) as additive. The effect of the content of Mg (NO3)(2)center dot 6H(2)O on the morphology, microstructure, surface chemistry, specific surface area and porous structure of the lignin-based porous carbon nanofiber films (LCNFs) is investigated. Results show that with the increase of the content of Mg(NO3)(2)center dot 6H(2)O in the spinning solution, the average diameter of fibers is decreased obviously, while specific surface area and mesoporosity are increased significantly. When mass ratio of Mg(NO3)(2)center dot 6H(2)O/lignin is 2:1, the resultant LCNFs possessed an increased specific surface area of 1140 m(2) g(-1) and a significantly improved mesoporosity of 78%, and showed hierarchical porous structure. LCNFs were cut into electrode for supercapacitors directly and were evaluated in three-electrode and two-electrode cell. With increase of Mg (NO3)(2)center dot 6H(2)O, the capacitive performance of LCNFs turn better. When mass ratio of Mg(NO3)(2)center dot 6H(2)O/lignin was 2:1, the specific capacitance of LCNFs reached 248 F g(-1) at 0.2 A g(-1), much higher than that of sample without Mg(NO3)(2)center dot 6H(2)O (173 F g(-1)). Moreover, LCNFs showed an outstanding rate performance (capacitance retention of 59-67% from 0.2 to 20 A g(-1)) and a good cycling stability (capacitance retention of 97% after 1000 cycles at 20 Ag--(1)).