Soft ground is often improved to increase strength and stiffness by methods such as jet grouting and stone column which result in heterogeneous ground with improved columns. Experimental methods (Standard Penetration Test, sampling and laboratory testing, etc.) used to assess such ground improvement are subjected to several limitations such as small sampling volume, time-consuming, and cost ineffectiveness. It's difficult to assess the average property of the improved ground and the actual replacement ratio of ground improvement. The use of seismic surface wave method (i.e. multi-station analysis of surface wave, MASW) for such a purpose seems to be a good candidate. But the surface wave method is essentially a 1-D method assuming horizontally-layered medium. What MASW measures in the highly heterogeneous improved ground remains to be investigated. This study evaluated the feasibility of MASW in the heterogeneous ground with improved columns and investigated the homogenization of shear wave velocity measured by MASW. The lateral sampling space of the surface wave testing was also investigated by field testings of different survey line locations relative to the improved columns. The engineering information that can be extracted from the improvement rate of shear wave velocity obtained by surface wave testing is discussed.