In this paper, the effect of sub-zero temperatures on the activation of basal slip, {101‾2} tension twinning and <c+a> pyramidal slip in pure magnesium was investigated systematically at the micron length scale using micropillar compression. The micropillar compression was performed inside an SEM on selected grains of commercially pure polycrystalline magnesium between room temperature and ~ −94°C. A cryo-stub was designed and successfully employed to perform micropillar compression experiments below room temperature. Post-mortem SEM and TEM showed activation of basal slip in 112‾1 oriented micropillars, {101‾2} tension twinning in 13‾20 oriented micropillars and <c+a> pyramidal slip in 0001 oriented micropillars. CRSSs were derived from the stress-strain curves as a function of test temperature for the three deformation modes. The CRSSbasal increased with decrease in test temperature for micron-sized pillars in comparison to an opposite trend for CRSSpyra: CRSStwin showed no change from room temperature to ~ −94°C.