Some weight loss accelerating agents, dodecyltrimethylammonium chloride(DTAC), dodecyltrimethylammonium bromide(DTAB), dodecyldimethylammonium chloride(DDBAC), polyoxyethylene(2) dodecylbenzylammonium chloride(PDBAC), and 1-(2-hydroxyethyl)-1-benzyl-2-undecylimidazolinium chloride(AEUIC), were synthesized. As a result of weight loss treatment of the weight loss accelerating agents with NaOH to PET fiber, the increase of weight loss was the order of PDBAC > DDBAC > DTAC > DTAB > AEUIC. Among the weight loss accelerating agents, AEUIC hardly showed weight loss effect, and it was separated into two layer in the NaOH solution at the treatment concentration above 6g/L, but POBAC showed good weight loss effect of 21% that approach almost to a theoretical weight loss, 21.6%, at the concentration above 8g/L.