Novel transition metal nitrides Of Co3N and Fe3N thin films have been successfully fabricated by combining reactive pulsed laser deposition and DC discharge in a nitrogen ambient. The electrochemical reactions of lithium with Co3N and Fe3N thin film electrodes were first investigated by the galvanostatic discharge and charge, cyclic voltammetry, and the in-situ spectroelectrochemical measurements. These thin film electrodes exhibited reversible discharge capacities ranging from 324 mAh/g to 420mAh/g. The structure, morphology, and composition of the as-deposited, lithiated, and delithiated Co3N and Fe3N thin films have been characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The observed diffraction peaks from metal Co(111) and Fe(110) in the lithiated thin films showed well crystallinity of transition metallic Co and Fe formed by Li reacted with Co3N and Fe3N, respectively, which could further be confirmed by their XPS spectra. We proposed a new reaction mechanism, in which part of the transition metallic Co and Fe formed during the first discharging is nitrided and another part as an active spectator may play a major role in driving the decomposition and formation of Li3N during the subsequent electrochemical reaction.