Abstarct: In systems analysis, uncertainties may exist in model parameters and input data. Those uncertainties can propagate through the analysis and generate uncertainties in systems analysis. Grey systems theory offers a method for incorporating uncertainties of interval plan network. In this study, a grey critical path method has been developed and applied to a case study of construction project planning. The developed method allows uncertain information presented as interval numbers, to be effectively communicated into the model formulation and the resulting solutions. The output reults are capable of refelcting potential system condition variations caused by the existence of input uncertainties. Results from the case study application indicate that reasonable solutions have been generated.