Capillary rise, drop-weight, pendant-drop and ring methods which are originally deve- loped for surface tensions have been adapted to the measurement of interfacial surface tensions. Dropweight method is, however, frequently employed for the purp se. interfacial tensions usually lie between the ’ndividual surface tensions of the two liquids in question. interfacial ten¬sions are cf extreme importance in connection with colloids, biological Systems and separation processes such as liquid extraction, mixed vapour condensation with an immiscible condensate. The interfacial tensions for the systems of toluene-water, benzene-water, n-heptane-wa- ter and cyclohexane-water have been determined över a temperature range of 20-80°C by the drop-weight method. The method that is described by Harkins (3) has been slightly modified to eleborate better experimental measurements. The relationship between the interfacial ten- sion and temperature has been correlated by the least square method for each of the systems.