Ensemble based Probabilistic Quantitative Precipitation Forecasts (PQPF) have been operationally created on a daily basis at NCEP since 1997. The PQPF forecasts are based on the relative frequency of ensemble members indicating a particular event. Since neither the numerical weather prediction model nor the ensemble generation technique is perfect, these probability values are not necessarily reliable. To ameliorate the problem a calibration algorithm to reduce the bias in the first moment of the ensemble based probability distribution has been developed and applied on an experimental basis. The calibration is based on the comparison of the frequency distributions of observed and forecast precipitation amounts over a 2-3 month preceding period, over the continental US. verification results indicate that the reliability and skill of the calibrated forecasts is significantly enhanced. Further improvement is expected from a second adjustment where the second moment of the ensemble is calibrated. It is expected that the PQPF calibration procedure will be operationally implemented, providing reliable and more skillful PQPF forecasts to the hydrologic and other user communities.