In Zhejiang province, the sensitivity of soil in Zhoushan area is up to 8 while the average value is 4 in Hangzhou, Wenzhou, Ningbo, etc. areas. In order to investigate the cause of such a high value of sensitivity of Zhoushan soils, experimental study on Zhoushan and Wenzhou sensitive soils was conducted and compared in this paper, including conventional geotechnical tests, the scanning electron microscope (SEM) observations of microstructure, the energy dispersive X-ray spectroscopy (EDS) composition analyses and X-ray diffraction analyses of clay mineral compositions. As compared with Wenzhou soils, the liquidity index of Zhoushan soils is larger, the structure of Zhoushan soils tend to be destroyed easier, the microstructures of Zhoushan soils tend to be more loose and disordered, the contents of chlorine and sodium elements are higher and the contents of clay mineral are also higher of Zhoushan soils. It is conducted that the sensitivity difference of Zhoushan clay and Wenzhou clay are caused by various comprehensive factors.