Diabetic foot ulcers are a significant complication in people with diabetes mellitus. The changes of mechanical properties of plantar tissues associated with diabetes may contribute to a high incidence of diabetic foot ulcers. This study investigated the feasibility of using three-dimensional (3D) elastography to measure 3D elasticity of the fat pad and then calculate 3D elasticity gradients of the foot. This method may improve the detection of people at risk for diabetic foot ulcer. Elastography with a soft ratio measurement may provide a visualization of plantar soft tissues for clinicians to diagnose foot ulcer risk. In this study, we measured B-mode and elastic ultrasound images at the first metatarsal head in five volunteers. The soft tissue contains four layers, including inner layer (Q1, near bone surface), sub-inner layer (Q2), sub-outer layer (Q3), and outer layer (Q4, near skin surface). The elasticity values were significantly greater in the Q3 layer compared to the Q1 layer. The elasticity gradient values were significantly smaller in the Q3 layer compared to the Q2 layer. The correlation between the elasticity and elasticity gradient was r = −0.88 in the Q3 layer.