Presented in this paper is an experimental investigation into the effect of long-term soaking on the decrease of total soluble salts (TSS) contents and distribution of moisture for compacted clayey gypsiferous soil. Two types (A and B) of clayey gypsiferous soils were used in this study. For each soaking period, two California bearing ratio (CBR) samples were prepared of type A soil and soaked under 70 and 10 lb (312 N and 45 N) surcharge loads suitable for highways. Various CBR soil samples of type B were prepared and soaked under 210, 140 and 70 lb (935 N, 623 N and 312 N) surcharge loads (suitable for airports) for the same soaking periods as type A CBR soil samples. For long-term soaking periods, a gradual drop in TSS (mainly gypsum) content took place at the top of CBR samples to reach a significant amount at the end of 180 days soaking. An empirical equation has been developed relating the initial total soluble salts contents to the total soluble salts contents after various soaking periods of CBR soil samples in the laboratory, taking into account the plasticity properties of the tested soils and the effect of surcharge load.