A theoretical study of the mechanism and kinetics of the reaction of 2-propargyl radical, H2CCCH, with ammonia, NH3, has been carried out by ab initio molecular orbital theory based on CCSD(T)/6-311++G(3df,2p)//B3LYP/6-311++(3df,2p) method. The potential energy surface (PES) for the C3H3 + NH3 reaction was established, showing that the reaction has four principal entrance channels. Two H-abstraction reactions from NH3, leading to propyne or allene + NH2. The addition reactions start by formation of two intermediates H2CCCHNH3 and H2CC(NH3)CH. From these two intermediate states, many other transition states and intermediate states can be accessed, leading to 21 possible products. The reaction has sizable entrance energy barriers, though the H-abstraction entrance channels might contribute significantly at high temperatures, where formation of HCCCH3 + NH2 is more energetically favorable.