Technically pure cobalt with a phase transformation temperature of 700 K was investigated by high temperature nanoindentation. From the results of constant indentation strain rate experiments as well as strain rate jump tests the rate controlling deformation mechanisms could be derived. For the low temperature hcp phase from room temperature to 450 K a bcc-like deformation behavior was observed, while from 450 K to 700 K it was found that dislocation cross slip bears plasticity. In the high temperature face centered cubic phase cutting of forest dislocations was identified as the dominating deformation mechanism.