The effect of material uncertainty on the robust design of a composite helicopter rotor blade is demonstrated. A first-order reliability method is used to propagate the material uncertainty through a finite element code for both cross-sectional analysis and sensitivity analysis. First-order sensitivity derivatives obtained by central finite difference scheme are used in the uncertainty propagation. The statistical moments are then used to perform robust design of composite rotor blade cross section with constraints on the cross-sectional stiffness. The variation of uncertainty effect with stacking sequence of the rotor blade are shown. The robust design results show 12-23 percent reduction in the standard deviation of flap and lag stiffnesses when compared with the standard deviation of baseline design.