Significant change in the cloud point of the nonionic surfactant solutions is observed by adding foreign substance. The aqueous solutions of these surfactants show complex phase behaviour including liquid-liquid separation at higher temperature. Electrolytes as well as nonelectrolytes have a large effect on the cloud point (CP) of C 12 EO 6 and C 12 EO 8 nonionic surfactants, because of their effect on water structure and their hydrophilicity. The presence of NaI and KI in the systems leads to a substantial increase in the cloud point of 2 wt% of the C 12 EO 6 and C 12 EO 8 solutions, but the increase is relatively less with KI than with NaI. Moreover, the cloud point decreases in the presence of NaF, NaCl and NaBr, and also similar identical observation was seen in the cloud point with KF, KCl and KBr, respectively. Furthermore, the results show that the addition of the tetramethyl ammonium bromide (TMABr) decreases the cloud point of the C 12 EO 6 and C 12 EO 8 , whereas the addition of tetrabutyl ammonium iodide (TBAI) increases the cloud point of the above systems. The clouding phenomenon of the aqueous C 12 EO 6 and C 12 EO 8 systems in the presence of various additives is discussed.