The detectability of the interannual variations of terrestrial water storage in 70 river basins acquired by satellite gravimetry was investigated using the Japan Meteorological Agency-Simple Biosphere (JMA-SiB) model. Terrestrial water storages for the monthly, seasonal, and annual averaging periods were computed from the output of a 10 year integration performed by the JMA-SiB model. The satellite specification was assumed to be the same as for the NASA Gravity Recovery and Climate Experiment (GRACE). The total errors in the satellite-gravimetry-derived terrestrial water storage (including the instrument error, atmospheric error, and error due to the postglacial rebound) were computed for each period at each basin. The standard deviation of the interannual variation with the total error for three different time scales, averaging monthly, seasonal and annual results, was compared precisely in the continentalscale river basins. The error-signal ratio (i.e. the ratio of the total error to the standard deviation) was used to assess the detectability. The results demonstrate that the gravity satellite missions can detect the interannual variations in large river basins in most years, but the gravity satellite missions can detect those in small river basins only with the probability of 1 year out of 3 years or more. These characteristics were found in all the three averaging time scales.