Extraction systems containing diisopropyl ether ( IPE) and high initial hydrochloric acid concentration ( higher than 7.1 mol/L) are very sensitive to temperature changes. Small changes ( a few degrees centigrade) in working temperature may cause changes not only of the phase volume but also of the number of phases. Results of investigation of the temperature effect over the interval of 15 to 40°C on the volume and number of equilibrated phases in the system hydrochloric acid - water - IPE -iso-pentyl alcohol as well on the distribution of hydrochloric acid are given. The observed effect of temperature is compared to that in systems containing n-pentyl or n-hexyl alcohol as a component of mixed solvent.