An intermolecular aza-Wittig reaction Ph3PNH + OHCCOOH --> Ph3PO + NHCHCOOH has been studied theoretically using ab initio calculations at the MP2/6-31G*//HF/6-31G* level of theory. We find that the aza-Wittig reaction used to form iminoacetic acid (NHCHCOOH) from (E)/(Z)-glyoxalic acid (OHCCOOH) involves low energy barriers (the two dominant barriers are 4.5/6.7 and 22.0/17.6 kcal/mol, respectively) and is exothermic (23.8/29.3 kcal/mol). We conjecture that the ease of the intermolecular aza-Wittig reaction could provide a new and efficient way of synthesizing imino acids.