One of the problematic soils in our country is weathered residual soil, and flow limit are frequently utilized as an indicator expressing the consistency of this type of soil. In recent years, on the other hand, landslide disasters caused by heavy rain and earthquakes are regularly occurring in the distribution area of some problematic soils, and when considering its effective use, it is necessary to grasp the characteristic of some problematic soils, and above all its compaction characteristic (maximum dry density, optimum moisture content). In this study, we carried out various laboratory tests on weathered residual soil, sandy volcanic ash soil, and volcanic cohesive soil, referred to as problematic soil, and performed an experimental investigation into the basic properties and compaction characteristic of some problematic soils. The result was that it was revealed that flow limit is an effective indicator expressing the consistency of some problematic soils, and this has a very strong correlation with compaction characteristic.