A basin-wide flood monitoring and warning systems is being implemented sequentially in river basins of the Philippines, which suffer from severe floods. The Cagayan River basin with draining area of 27,280km2, that is the largest river basin in the Philippines, has five rainfall and water level gauges for the purpose of flood monitoring and warning. Despite the installed monitoring system, an operational flood forecasting model based on physical theories has not been performed for this basin. Then IFAS, a distributed hydrological model developed by ICHARM, was applied to the Cagayan River basin as a flood forecasting model. One of its notable functions is the capability of using both ground-gauge data and global satellite information, such as topography, land use, and rainfall in the model. This global satellite information is utilized as supplementary information to facilitate easier forecast of flood discharge in an insufficiently-gauged river basin. On the other hand, little has been addressed about accuracy validation of global satellite information as input data of the flood forecasting model. Therefore, GSMaP provided by the Japan Aerospace Exploration Agency (JAXA) was applied to the flood forecasting model as a rainfall input. The comparison shows ground rainfall excels at accuracy of quantity, whereas GSMaP excels at spatial distribution. As a result, the study found that simulation with calibrated GSMaP can reproduce river discharge with high accuracy, suggesting that satellite information combined with ground gauged data is applicable and effective for flood forecasting in the Philippines.