This study investigates the effect of uncertainty in composite material properties on the cross-sectional stiffness properties, natural frequencies, and aeroelastic responses of a composite helicopter rotor blade. The elastic moduli and Poisson's ratio of the composite material are considered as random variables with a coefficient of variation of around 4%, which was taken from published experimental work. An analytical box beam model is used for evaluating blade cross-sectional properties. Aeroelastic analysis based on finite elements in space and time is used to evaluatethehelicopterrotorbladeresponseinforward flight.Thestochasticcross-sectionalandaeroelasticanalyses arecarriedoutwithMonteCarlosimulations.Itisfoundthatthebladecross-sectionalstiffnessmatrixelementsshow acoefficientofvariationofabout6%.Thenonrotatingrotorbladenaturalfrequenciesshowacoefficientofvariation of around 3%. The impact of material uncertainty on rotating natural frequencies varies from that on nonrotating bladefrequenciesbecauseofcentrifugalstiffening.Thepropagationofmaterialuncertaintyintoaeroelasticresponse causeslarge deviations, particularly in the higher-harmonic components that are criticalfor the accurate prediction of helicopter blade loads and vibration. The numerical results clearly show the need to consider randomness of composite material properties in the helicopter aeroelastic analysis.