Grain　reduction　and　the　rate　of　grain　refinement　as　a　function　of　the　processing　conditions　of　constrained　groove　pressing　(CGP)　for　a　Cu-38Zn　alloy　is　investigated.　It　is　found　that　during　the　early　stage　of　CGP　more　effective　grain　refinement　can　be　achieved　using　the　pressing　die　with　narrower　groove　widths.　Similarly,　during　this　stage　the　cross-orientation　pressing　procedure　results　in　finer　grains　than　the　single-orientation　pressing　procedure　even　though　both　pressings　have　the　same　plastic　strain.　However,　the　grain　sizes　from　different　pressing　conditions　merge　at　large　plastic　strains.　These　phenomena　have　been　interpreted　based　on　the　complexity　of　the　deformation　field　and　the　change　of　the　dislocation　generation　rate　over　multiple　pressing　cycles.　The　result　of　this　study　demonstrates　that　the　rate　of　grain　refinement　is　affected　by　the　complexity　of　the　deformation　field.　©　2009　Acta　Materialia　Inc.