This paper focuses on the uncertainty due to parameter variabilities in the food chain model and the ingestion dose calculation of the radioecological model ECOSYS, which is the basis of the food chain and the dose module in the European decision support system RODOS. Investigations on parameter sensitivity and model uncertainty are performed by applying a Monte Carlo method with Latin Hypercube sampling. The uncertainties of predicted contamination of foodstuffs as well as the uncertainties of dose predictions are estimated taking into account the correlations between parameters. Both, the sensitivity of model parameters and the uncertainties of model results are dependent on the actual radioecological situation; important factors are especially the type of radionuclide and the time of year when the deposition occurs.