This study attempted to identify substances that are driven out of HEK293 cells by methylmercury. Metabolomic analysis revealed that the levels of 3-phenylpropionic acid, citrulline, lactic acid, ornithine, proline and beta-alanine in the cell culture medium were increased by the treatment of cells with methylmercury. Address to the mechanism underlying the release of these substances will provide useful information to elucidate the toxicity mechanism of methylmercury.