Ni-Cr-Fe-Co-Mn-Mo medium/high entropy model alloys with stacking fault energies less than 25 mJ/m2 at room temperature were prepared to study the deformation twinning behaviour or mechanism. The deformation behaviours of the alloys were investigated by tensile tests at temperatures of -196°C, RT and 300 °C. Some alloys show an increase in elongation from about 50% at RT to about 90% at -196C and simultaneously a significant increase in tensile strength. The microstructures in the deformed material and twinning mechanisms were studied using SEM EBSD and ECCI techniques. Occurrences of deformation induced twinning have led to twin induced plasticity, TWIP effect. The present work increases the knowledge for the development of high entropy alloys with a combination of high strength and high ductility.