The shear strength behavior of volcanic sandy cohesive soils is of considerable interest as they are extensively distributed in Aomori Prefecture, Japan. To understand this behavior, triaxial undrained compression testswere conducted on undisturbed sandy cohesive soils under unsaturated conditions. Initial matric suctionwas set as 0, 50, and 90 kPa, and confining pressures (net normal stresses) were set as 0, 10, and 100 kN/m2. Then shearing processes were done under undrained conditions. The mechanical behavior (i.e., strength and volume change behavior) is explained using the experimental results. The focus of the present study was directed towards understanding the influence of soil structure on the shear strength behavior of volcanic soils under unsaturated conditions.