Diabetic foot is a common complication for people with diabetes but it is unclear whether the change is initiated from the skin surface or underneath plantar tissues. This study compared the thickness of epidermis and the thickness and stiffness of the total plantar soft tissue among people with diabetes with or without complications. Seventy-two people with diabetes, including 22 people with neuropathies, 16 foot ulcerations, 34 pure diabetics without complications and 40 healthy controls participated in the study. The thickness of the epidermal layer of the plantar skin was examined using high-frequency ultrasonography; the thickness and stiffness of the total plantar soft tissue were measured by using tissue ultrasound palpation system at the big toe, the first, third and fifth metatarsal heads; and the heel pad. Compared with the control group, the average epidermal thickness of plantar skin was reduced by 15% in people with diabetic foot ulceration and 9% in people with neuropathy, but was increased by 6% in pure diabetics. There was an 8% increase in total thickness of plantar soft tissue in the 3 diabetic groups at all testing sites (all p < 0.05), except the first metatarsal head. The stiffness of plantar soft tissue was increased in all diabetic groups at all testing sites compared with the control (all p < 0.05). The epidermal plantar skin becomes thinner and plantar soft tissues stiffen in people with diabetes, particularly in persons who have neuropathy or ulceration, which increases the risk of tissue breakdown and ulceration formation.