Gypseous soils are distributed in vast areas and various regions of Iraq and other countries. Many foundation failure problems that occur in these soils are associated with percolation of water and dissolution of gypsum. Many attempts were made by several researchers to treat and improve the properties of gypseous soils to decrease the dissolution of gypsum and collapse potential of these soils. The purpose of the present work is to investigate the effect of dynamic compaction process on the behaviour of gypseous soils. Extensive laboratory tests are carried out to study the geotechnical properties and the behaviour of three gypseous soils of different gypsum contents; 60.5, 41.1 and 27 %. The tests included compaction characteristics, compressibility, and collapsibility tests for samples tested before and after treatment by dynamic compaction process under different number of blows, falling weights and heights of falling of the weights. Three weights are used to compact the samples, namely; 2, 3 and 5 kg. The number of blows is varied between 20 and 40, while three heights of drop are tried (35, 50 and 65) cm. The results showed that the best improvement in compressibility is achieved when the sample is compacted by 20 blows; above this number a negligible decrease in the compression index C C is obtained. As the gypsum content increases, the dynamic compaction has greater effect on improvement of compressibility of the soil, while as the height of drop increases, the compression index C C decreases.