Abstract: Variables needed for hydrologic design of hydraulic structures include the rainfall intensities, critical storm duration (concentration times for determination of peak discharges) for the catchments area, and the selected frequencies (return period). These variables together constitute the design storm. In this study, the relationship between the rainfall amount, duration and frequency are studied for Mujib basin in Jordan. Intensities-Duration-Frequency (IDF) equations were developed for each of the 8 rainfall recording station in the basin. The 8 IDF equations obtained were compared with the curves obtained by Gumbel method and Water Authority of Jordan (WAJ); the results predicted by the writer are closer to the measured values. There are some differences in the results between this study and the studies of other investigators; these differences are due to: differences in the record length used by this study and WAJ study; extrapolation of WAJ curves to include the 5 min duration and some of the relative error was due to small values of reading. Peak discharges were calculating for different location in the basin; it was found that the peak discharge which gotten from Manning`s equation is closed to the peak discharge that gotten from rational method at recurrence interval equal to 25 years.