A pot experiment was conducted in a glasshouse to clarify and quantify the effect of soil water regimes on dry matter production,water-use efficiency (WUE),and carbon isotope discrimination (CID) of different plant parts of upland rice (Oryza sativa L.) measured at the tillering and maturing stages,and to understand the relationship between WUE and CID.Three water regimes were imposed: saturated condition (W1),70% of saturation moisture (W2),40% of saturation moisture (W3).Results of the experiment showed that biomass accumulation decreased by 45% at the tillering stage,and by 16%~19% at the maturing stage with soil water regime changing from W1 to W2,and by 73% and by 55%~57% with soil water regime from W1 to W3.On the other hand,above ground dry matter-based WUE (WUE_A) and total dry matter based WUE (WUE_T) increased with rising water stress by 0.07~0.28 g kg^-1 at the tillering stage,and by 0.07~0.45 g kg^-1 at the ma turing stage.The values of CID of the plant varied from 17.0 to 20.6 with significant differences among plant parts,which can be lined in an order of rootCID values of all the analyzed plant parts significantly decreased with rising water stress.A consistent negative relationship between the CID values of leaves and WUE_A(and WUE_T) was ob served.