After above-knee amputation, the biological knee and ankle are replaced with prostheses. The mobility level of individuals with amputation is related, in part, to the functionality of their prostheses. To understand healthcare needs of amputees, as well as design new, more helpful prostheses, we need to understand the biomechanical effects of using current prosthetic devices. Here we present a dataset of kinetic, kinematic, electromyographic, and video recordings of nine above-knee amputees during the stand-up and sit-down movements. This dataset represents the first repository of amputee biomechanics during stand-up and sit-down with their passive, microprocessor-controlled prostheses, which are still the standard of care after above-knee amputation. The biomechanics were captured using a 12-camera motion capture system with two force plates and four EMG sensors on the intact lower limb. The dataset can serve as a reference when designing next-generation powered prostheses and controllers, to inform prosthetic prescription, and to improve amputee rehabilitation.