During earthquakes, dynamic loads caused by inertia forces are applied to ground improvements by deep mixing method. Therefore, the internal stability of cement-treated soil ground subjected to the seismic loading should be examined in the seismic design of the ground improvement. The speed of the loading caused by the inertia forces during earthquakes is much faster than that in the standard unconfined compression test. It is well known that the loading speed affects the strength of materials. Therefore, the strength under the rapid loading conditions is required to design the ground improvements rationally. The unconfined compression tests of cement-treated soils were conducted under the rapid loading conditions in this study. The rapid load in the shape of a solitary wave is applied to the specimens. The unconfined compression tests with the strain rate of 1%/min were also conducted for comparison. The experimental result indicates that the rapid loading increases the strength by about 20% as compared with the strain controlled loading. The test results were analyzed with the statistical manner to evaluate the variation of the strength of the cement-treated soil specimens prepared in a laboratory. The statistical analysis provides the good understanding of the influence of the data variation on the relationship between the strengths obtained from the rapid loading and strain controlled tests.