We measure the strain rate dependence of 0.2% offset yield stress in single-crystal nickel nanowires with diameters ranging from 80 to 300 nm. In situ tensile experiments with strain rates from 10 4 s 1 to 10 2 s 1 were conducted, and the small activation volume ( 10b3, where b is the Burgers vector length) and high strain-rate sensitivity ( 0.1) were obtained. These results agreed with atomistic simulations. Our work provides insights into the strength-limiting and rate-controlling mechanism of plasticity at the nanoscale.