The Burgers vectors, the associated slip plane and the morphological feature of dislocations activated in B2-type CoZr and CoHf polycrystals were investigated by means of bright and dark field transmission electron microscopy (TEM). In both intermetallic compounds, CoZr and CoHf, the slip systems were determined to be <100>011 at whole testing deformation temperatures. It was also shown that the <100> dislocations activated in both CoZr and CoHf were not dissociated. Based on these TEM observations, the micro-mechanism associated with the strength anomaly generally observed in IVa-VIII B2-type intermetallic compounds is briefly discussed.