In this paper, a thermocouple psychrometric technique is used to measure soil suction and assess the reliability of a swell pressure prediction method. Kaolinite-bentonite clay mixtures were prepared to obtain expansive soils with a wide range of plasticities. Suction measurements using thermocouple psychrometers and constant volume swell tests in oedometers were made on statically compacted :specimens. Soil suction-water content relationships were evaluated. The results indicate a linear relationship between the logarithm of initial soil suction and swell pressure measured in the oedometer. it has been shown that the method proposed by Johnson & Snethen for the prediction of swell pressure using suction measurements overestimates the ultimate swell pressure.