A study was carried out on the effects of the addition of sand on swelling clays from the Far North Region of Cameroon is studied. Results of Modified Proctor tests performed on the samples of mixtures of sand and swelling clays in Maroua and Fotokol showed that their dry densities increase as the sand content increases. The optimal dry densities of experimental curves of mixtures according to the contents of sand added are in the shape of an inverted bell, which indicates the existence of an optimum content of sand added. The main results that could be drawn from this study were as follows: the optimal content of the added sand is 30% for the swelling clay in Maroua and 20% for that of Fotokol. For the optimum values of the levels of sand, the increase of optimal dry densities is about 7.4% for the corresponding water content values of about 9.00% to 9.95%.