A study was carried out to determine the cation composition in soil solution of two soils commonly cultivated with rubber (Rengam and Munchong series) and their relationships to exchangeable cations. The concentration of the cations in the two soil solutions is generally less than 0.5 cmol (+)/kg. The soluble cation concentrations are higher for Rengam soil, an Ultisol than for Munchong soil, an Oxisol, for all the cations studied, viz Ca2+, Mg2+, K+, Na+ and Al3+. Low concentrations of soluble cations result in soil solutions with low ionic strength. The ionic strength of the two soils is less than 0.008 M, with the ionic strength of Rengam soil being higher than that of Munchong soil. A good correlation was observed between soluble and exchangeable cation concentrations. The percentage of exchangeable cation which is readily solubililsed is low. The differences in availability of the cations in soil solution are attributed to the clay mineralogy of the inorganic soil colloids.