In　the　present　study,　the　room　temperature　mechanical　properties　of　nanocrystalline　Ni　and　Ni-75　wt-%Co　alloy,　prepared　by　pulse　electrodeposition,　were　contrasted.　Both　higher　strength　and　higher　ductility　were　obtained　for　the　Ni-75%Co　alloy　with　a　dual　phase　structure　and　an　average　grain　size　of　7·2　nm.　By　means　of　TEM　observations　of　grain　structures　before　and　after　tensile　deformation　for　Ni　and　Ni-75%Co　samples,　a　link　between　the　ductility　and　the　variation　of　stress　induced　grain　growth　during　tensile　deformation　was　established.　Observations　of　TEM　showed　stress　induced　grain　growth　during　tensile　deformation,　subjected　to　very　high　stresses　and　large　strains,　is　very　insignificant　for　the　Ni-75%Co　alloy　in　sharp　contrast　to　the　significant　stress　induced　grain　growth　occurring　in　Ni.　It　was　proposed　that　suppression　of　stress　induced　grain　growth　during　tensile　deformation　can　delay　and　even　prohibit　formation　of　shear　banding　plastic　instability　and　thus　enhances　uniform　strain　leading　to　an　enhanced　ductility.　©　2011　Institute　of　Materials,　Minerals　and　Mining　Published　by　Maney　on　behalf　of　the　Institute.