Fe-20Mn-3Cu-1.3C　steel　with　grain　sizes　of　18.12,　24.56　and　47.00　μm　was　prepared　by　hot　and　cold　rolling　and　then　holding　for　10　min　for　recrystallization　at　950,　970　and　1050°C,　respectively.　With　the　increasing　of　the　grain　size,　the　value　of　microhardness　of　the　steel　decreases.　The　steel　hardness　increases　after　deformation　due　to　strain　hardening,　and　the　amplitude　of　increase　in　hardness　after　deforming　is　larger　for　the　steel　with　coarse　grains.　At　low　strain　stage,　the　working　hardening　rate　decreases　substantially　with　true　stain　and　similar　strain　hardening　exponent　is　observed　for　the　steel　with　different　grain　size.　At　high　strain　stage,　the　work　hardening　exponent(n)　increases　more　considerably　in　the　steel　with　larger　grain　size.　Analysis　shows　that　dislocation　gliding　and　twinning　deformation　are　the　primary　deforming　mechanism　at　low　and　high　strain　stage,　respectively.