Electroreduction of oxalic acid (OA) is an effective process to produce glyoxylic acid (GA). However, electrochemically generated GA solution is yellow, which lowers the quality of GA and affects the application in producing the downstream products. It is urgent to investigate the composition of chromogenic substances (CSs) and separate them from the GA solution. In this work, the presence of tartaric acid, glyceric acid, and pyruvic acid in the electrochemically generated GA solution is successfully confirmed by high‐performance liquid chromatography‐electrospray‐mass spectrometry. Tartaric acid is originally generated from GA and glycolic acid, and then further reduced to obtain chromogenic glyceric acid and pyruvic acid. 92.97 % of CSs could be successfully removed from the GA solution by electrodialysis at 240.64 A/m2 and 25 °C. A separation of OA and GA is also achieved by electrodialysis. This study makes a significant contribution to the industrialization of electroreduction process to prepare GA.