High-frequency ultrasound has realized high-resolution observation of deep part of the dermis in vivo. The size of sebaceous glands was evaluated by three-dimensional ultrasound microscopy with the ultrasonic frequency of 120 MHz. The viscoelasticity of the same regions was measured by well-established biomechanical equipment. There was no significant difference between the size of sebaceous glands in cheek and forearm. The skin's ability to recover to its initial position after deformation was significantly higher in forearm than in cheek. Both sizes of sebaceous glands in cheek and forearm were positively correlated with the parameter of viscoelasticity. The size of the sebaceous glands in the deep part of the dermis can be a parameter of skin viscoelasticity. High-frequency ultrasound imaging contributes to the evaluation of human skin morphology as well as functions.