A highly sensitive electrochemical sensor for the detection of ascorbic acid (AA) was first fabricated using network-like carbon nanosheets (NCN) as an enhanced electrode modifier. Novel carbon nanosheets were synthesized from willow catkin via a high temperature carbonization and chemical activation process with the aid of potassium hydroxide (KOH). The formation of porous and interconnected structures of the resulting product was characterized by various experiment techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and nitrogen isothermal adsorption–desorption technique. The network-like carbon nanosheet modified glassy carbon electrode (NCN/GCE) exhibited excellent electrocatalytic activity for the electrochemical oxidation of ascorbic acid owing to the unique network-like and partially graphitic structure. The amperometric curve of AA on the NCN/GCE showed a quick current response, a fine linear consistency of the peak current with the concentration of AA, a low detection limit and an excellent selectivity. Based on these excellent properties, a new sensing platform was developed and verified by the determination of ascorbic acid in commercial injections.