This　paper　proposes　an　improved　zonotopic　method　to　set　membership　state　estimation　for　nonlinear　discrete-time　systems　with　a　bounded　description　of　noise　and　parameters.　According　to　the　previous　method,　a　zonotope　containing　the　uncertain　trajectory　of　the　system　is　computed　using　interval　arithmetic　in　the　time　update.　In　the　observation　update,　an　improved　intersection　algorithm　of　zonotope　and　strip　is　used　to　obtain　a　zonotope　bounding　the　intersection　of　the　uncertain　trajectory　with　the　region　of　the　state　space　consistent　with　the　observed　output.　This　obtained　zonotope　is　used　to　describe　the　feasible　solution　set　of　state.　It　is　proven　that　the　zonotope　obtained　by　the　improved　algorithm　can　be　tighter　than　the　one　obtained　by　the　previous　algorithm.　Simulation　experiments　are　conducted　showing　the　performance　of　the　improved　state　estimation　method　as　compared　with　the　previous　one.　Two　types　of　noise　distribution　are　considered.　The　results　expose　the　weakness　of　the　previous　method　and　illustrate　the　effectiveness　of　the　improvement.　Copyright　(c)　2012　John　Wiley　&　Sons,　Ltd.